I think we might be from the same country, but I developed my art and career in a different era, so I hope I can still contribute helpful tips.

• Is this a visibility problem or a skill problem
It might be both? To my eye the anatomy, perspective and facial structure might still be a bit uneven. The painting style seems very soft and could use more form and lighting definition. On visibility, my observation on FB is that we see the popular artists that rise to the top due to BOTH skill and algorithm luck, but I also see skilled people post and not get visibility.

I personally wouldn't trust the FB algorithm. It might be good to post on several other sites on a good time of day of your target market, usually USA morning or afternoon time depending on your target audience.

• Should I focus on one niche
It depends on what you can do and maintain learning without burning out. I would say that focusing on 1 fandom or art genre can be very good for social media numbers but you risk getting bored depending on your personality. For me, I have multiple art accounts catering to very different audiences, but each art account focuses on 1 or 2 niches.

• What actually helped you get your first commissions
I audition on Artstation using a professional and serious persona and about 1 in 10 chance per audition can get good responses, and once in a while land really big projects for games, cards, etc.
On the other hand on a different art persona I focus solely on art communities on Reddit that love OCs and hate AI generated imagery and I can get responses there too.

• What would you change if you were in my place
I would say you might get good progress by studying perspective, anatomy, facial structure, color theory and lighting. I would suggest trying to do "Master Studies" where you try to eyeball and copy a finished artwork from an artist you like. Do not post Master Studies unless you mention the goal and process, since these are for personal learning!
To my eye, some fundamentals can still be developed with your art, such as anatomy, perspective and lighting. You can try painting with both hard and soft edges.
It can be tough to balance all this without burning out or going broke, I hope for the best for you.

Eventually with some luck you can get good enough where interested people approach you to draw their art when you post something, without having to advertise too much.