What you are really asking is, how to do this with no budget, aren't you ;-)
Because if you have budget, the answer is easy: Hire experts and have a budget for this. That's effective.
There are many threads about this question. But as far as I know, no one has come up with a one fits all solution that works. Promoting a game is not easy.
I see multiple things that might be done for passive promotion for your game. But the cheapest active promotion, apart from being super lucky, would be to find a streamer playing your game, and the game being appealing to the target audience to begin with. So you need something that holds the promises you make in advertisement. Unfortunately, the streamer that did play your game is not really famous.
Thoughts that came to mind, when glancing at your game. (There is only rethorical questions in there)
Why is this for free, if you worked 10 years on it. There is a certain expectancy for free vs paid games. It's different on Itch than on Steam, because of the publishing hurdle Steam has, but in general, the price of something does set a base level of what you will expect and how you will interpret the circumstances. Of course it helps, if the game will deliver what is promised by the price. You will see a lot of cheap rpg maker games on Steam. There is an audience for this. And there is an audience for things that are African, even fake stuff like Black Panther.
So if you consider the game to be as professional as those $ 2-5 rpg maker games on Steam, maybe consider a separate premium release with some extra goodies.
The description and tags are missing how this is an action adventure game and not a typical rpg maker game (unless I am mistaken). This is a huge problem, if this is not clear. People looking for rpg maker games will be disappointed and people that do not like the rpg maker combat style will not give a second look, since they think it is one of those.
That boils down to the general advice to be appealing to your target audience. But for that your target audience has to recognise the game for what it is and find it under appropriate search terms via google and appropriate tags on Itch browsing. And if they glance at the cover and even hover over the cover and see the screenshots, that should be very clear and be highlighted. If all you highlight is the fact that this game features African culture in an educational way .... does that sound like a fun game or like some school lesson in disguise? Do you want to appeal to parents or to people looking to play a game that is not the usual fantasy tropes? Perhaps the first adventure game themed around African art and cultures.
Look here for inspiration https://itch.io/games/tag-action-rpg/tag-rpgmaker . Be it tags used, or how pages might look. Including screenshots. How do people highlight the cool features of their games.
My impression of your screenshots was not good. I have no clue what all this is supposed to be, and how the game is supposed to be fun based on these pictures. Yes I know, that's super hard to capture. There's a reason why there are people that get paid to do such things.
You could include animations how the character does some moves. Or dialogue with interesting npcs you will meet. An example puzzle. Show a skill tree or how you improve the protagonist. Images that look more interesting than holiday pictures of your relatives that they forced on you.
The title of the game. I do not know what it means, what it could mean, what it is supposed to mean. Not even after reading the game page. For some, that might make the game mysterious and they get get curios. For me, that just means the developer could not bother to make an actual title that would be helpful. If I google Nsala, I mostly get a fish soup recipe, so there is that. Maybe consider adding a subtitle or at least changing the one liner that appears below the title. The one where you currently hightlight that african cultures appear as a theme.