On a platform with a sane and reasonable search feature, sure, maybe. But that's not what we're dealing with; we're dealing with a platform where you can only filter content by adding more tags.
On itch.io specifically, it seems pretty easy to find both, just sorta mixed in with each other randomly, especially among the highest rated stuff. But the problem isn't even really, ease of finding what we're looking for. It's a matter of, excluding what we are explicitly not looking for. Let's take a look at the current top two rows of highest rated free nsfw web games, and what we can guess from their title cards:
1. Max the Elf: Looks straight at first glance? Then at second glance, nope, you can see screenshots of the male player character on the receiving end of cocks. Did not want to see that, did anyway. LGBT is right there in the tags, coulda avoided that with tag exclusion.
2. Sileo: Tales of a New Dawn: Looks gay, explicitly states that it is. Okay, cool, that was straightforward! Not gonna click it.
3. Five Nights at FuzzBoob's: Looks straight, judging by how the title card is literally just a pair of breasts. Haven't played it myself though so I can't be sure. After a brief look at the description though, I see the phrase "her two girlfriends", so... lesbian, then? Not seeing any tags to indicate this, though!
4. Superstition S1: From the title card, I can't even guess. I was even on the verge of suspecting it was one of those things that gets called "nsfw" for reasons like, horror or trigger warnings or some such thing? In the description though, I saw "Play as male, female, or non-gender specific, along with transgender choices.
Romance one of five characters, have flings, or stay single because life is hectic enough as is.", so... optionally LGBT, optionally straight? No way of guessing that without checking first, though.
5. Factorial Omega: My Dystopian Robot Girlfriend: Looks straight... and actually is!
6. After Years: Appears to be another obviously gay one.
7. Bad Ritual: Another where I can't even guess. Upon closer examination, LGBT and LGBTQIA are in fact in the tags (hey, there's a 5th gay tag!). No indication in the description whether it is gay, lesbian, transgender, or something else, but from a brief look at the comments it seems probably gay... unless it's actually bi and everyone is just focusing on the male characters.
8. The Forest of Love: Can not even guess from the title card. Or from the description. There is no LGBT tag in here. And yet, it seems that there is stuff with both male and female characters? So, this one is apparently bi, but just, poorly indicated in general?
9. Crown of Exile: No indication from title card. This one appears to have the ability to play as male or female, and romance male or female characters. No idea whether your own character's gender limits your options or not, though; there is no LGBT tag, but we already know that isn't completely reliable.
10. Some Sword/Some Play: Another with no indication from title card. Sifting through the description though, I see: "All three main romances are playable as any combination of M/F/NB with any configuration of naughty bits.". So, another that could be straight, gay, lesbian, or anything else depending on what the player chooses. No tags to indicate this.
11. He Fucked the Girl Out of Me: Can't guess from the image, but from the name, I would guess some sort of transgender thing? In the tags, I see: "Gay, Lesbian, LGBT, Queer, Transgender, Yuri". Wow that's a lot... okay we've gone from 5 all the way up to 8 gay tags thanks to this one. But: the description also states "Trigger Warnings are listed in-game.", and from the comments I am not even sure if this one is porn at all, but rather a deeper story which just happens to focus on nsfw subject matter?
12. Nicole's Risky Job: Would guess straight. Seems to actually be solo female though, no males involved, which means... would probably be equally fine for a lesbian as for a straight man. And would not be fine for a straight woman.
So, out of just these 12, that's quite a few incorrect guesses and stuff that is just poorly indicated without playing. Seriously, this is even worse than I thought, only like a third can be correctly guessed ahead of time without clicking on them. At this point, additional tags, even without the actual tag exclusion we all want, would be helpful for filtering for everyone.