I dont wanna spend money on ads.
I will second the use of social media. It's worked for me on https://matthornb.itch.io/ but it isn't the only way to go. It's part of a broader effort that in my case has involved trying everything I can think of and doubling down on anything that sticks. In my case I'm trying to actually sell some of my stuff, cheaply, but sell nonetheless. Some of it's free but most of my work is set up at a price of a dollar or two.
If you (whoever's reading at the moment) , as seems perhaps to be the case for the OP, are not interested in making sales, you just put together a small free game, and want somebody to be aware it exists, that is one thing. In that case, what follows may be total overkill. But for anyone here who seriously intends to make a substantial, well-built indie game or games, and is trying to sell it, this may be useful to you:
Ultimately if you believe your game is good and genuinely deserves to be noticed, you should not find it too hard to promote it.
Start with social media connections you already have, along with in person connections. Find related communities and groups and post there. Be an active user, comment, be helfpful where possible so you're not merely spamming.
Find communities that are actually likely to enjoy the game you made. The suggestion's been made to go for users of the same game engine, but that's a way of connecting with game developers, not the wider base of actual game players. Search for player communities first, not other game devs, though the game devs are certainly potentially useful in giving assistance and advice from a development POV.
I'm odd that way though - so far most of my released content has been designed to be of interest to game developers, not players. As such, talking to game devs actually makes sense for me. If you're selling a game, that's one thing - but if you're still working on game dev, as I am, and what you've actually ALREADY RELEASED is asset packs (seamless texture packs, 3d asset packs, etc) that are mainly useful for 3d artists, level designers, game developers, not players, then the logic of interacting with game devs becomes more clear.
Consider cutting a game trailer together, that showcases best aspects of your game - post it on YouTube with a link to the game page. This can drive traffic in a big way if the trailer is good.
Consider also messaging smaller but relevant Youtubers who are into your genre of game, see if any of them would be interested in it. You'll get mostly no response, but now and then someone might actually do a Let's Play of your indie title and that too can result in attention from the public.
Know that even if your ad budget's nonexistent, there's always some sort of grindy way of pouring time in rather than money. I've churned through the posting of literally 500+ Youtube comments in the last year or so, and this has a VERY LOW effectiveness but there's always someone out there, wasting time reading those. But having posted those for about a dozen hours across hundreds of relatively well-selected videos with viewers who may have actual interest in what I'm saying, the outcome has had an effect in pure traffic terms, similar to spending $20 in an optimized way, on ads. I know this because I also spent money on ads a few times. Basically if you do YT commenting that way, it pulls in maybe 15 click thrus per hour spent commenting. Not great, and it'll be a slow burn - many of the click thrus will arrive in the weeks or months after the comment's posted, not the first hour or day.
I spend on ads in a mix of different spots, trying to hit the right audiences. I used to love a particular slot on the now-defunct banner exchange 'Project Wonderful' and I'd hold that slot 24/7. For a price of $0.02 daily, I could have that tiny banner position and run my best-designed banner ad on it for that size, and get 8-10 clicks on that slot EVERY DAY. From real people, no less. That's almost unheard of - and it took me some messing around before I found it. I was grabbing 4 or 5 visitors per penny spent. To have traffic that cheap that's not bots is extremely rare, most of the time the cost per click thru is going to come out to $0.20, give or take, across most major ad systems. But if you are able to find an out of the way advertising system you can possibly save some doing that. Everyone immediately thinks of Google, Meta, Bing, etc... but the ones nobody's considering can in some cases be better. Banner ads broadly are considered dead, but if you find the right site that has a related audience, and your ad design's good, it can still work and be cheaper precisely because nobody much is using that format anymore.
Other than all that - the ad campaigns are absolutely useless if you're advertsing something nobody finds intriguing. So make your game look and sound great. Visuals are the #1 first thing people will notice about a game, and while ultimately gameplay will keep them playing, the graphics are often what gets them to give you a chance in the first place. Is it fair? Not really, but it's pretty much the reality. Also make sure you hit the sweet spot of conveying your premise well, specifically what exactly makes your title a bit unusual, what makes it stand out as different from other titles in the same broader category.
It may be the game's story having a unique hook, maybe it's a rare game mechanic that's super creative, maybe it's just the art style being uncommon.
When I began a couple of my projects (Miniature MiniGolf, Miniature Multiverse) I realized the core game design foundationally was never that special, just a good if relatively typical example of the respective categories. What made these titles stand out as unusual was the fact that every single scene in each of them was handmade out of O scale minis using detailed, fairly realistic model-railroading style techniques. So that's something odd which immediately grabs attention when everything else is going for standard 3d.
Top-down/isometric view minigolf where the courses actually are built using miniature art assembled on a table top?
Or a loosely 'Myst-like' adventure game, 360-degree panoramic UI, but all the worlds and settings you explore are built by hand, highly detailed in that particular way, and have a similarly tactile look?
No, you might argue, not unprecedented, but at the time I started these two projects I think the only remotely similar thing of any kind that yet existed was a semi obscure '96 title, "The Neverhood' - the visual design of which was made entirely from polymer clay. Only since I started have others started also jumping into the idea of, 'traditional miniature art in a video game' as seen in titles like Armikrog, Lumo City, and Truberbrook. What continues to hold uniqueness in my adventure game is it's still first-person - and so far the others with similar aesthetics are not.
So think about whatever it is that can make your game stand out. And make that your message. Have an 'elevator pitch' prepared for your game, that is... figure out how you'd describe why it is special in just a short phrase. And then use that phrase or similar, as the core of your promotional campaign, be it comments, social media posts, heck, even the game's website. Know people will often drift off after a few seconds even if they do click a link so try - if you can - to grab them in those first few seconds so they keep reading. Start strong, fill in details below that. Have trailer, screenshots, and any other elevant visuals accessible. End with a request from the visitor to the page. Not a pile up of a ton of options - focus on one core thing, which is getting them to play the game or if the game's not done yet... persuading them to wishlist it somewhere (usually Steam)
And yes, seriously do consider making your work available on multiple storefronts, not just itch. SO MANY PEOPLE USE STEAM. It's a mistake to ignore that audience.
Most simple bit af advice I can give is: think about how you'd respond if the exact same game came out, but made by someone else. Would you be aware of it? If not, why not, and what can you do about this? Once you were aware of this, would you want to investigate it further? If not, why not, and what can you do about this? Once you investigated it further, would you want to buy it? If not... you get the idea ;)
I had an instagram (about minecraft builds lol) where I got hundred of followers in a week because I followed minecraft builders that I liked. Completely natural growth in my opinion. The hashtags worked a bit but really it was peoples curiosity and appreciation for each others work that made them click follow