It seems the game was more popular in 2007, when the Little Golem 13x13 championship #15 had 200 participants. The last edition #54 had only 59 participants. (Yes, more tournament types and board sizes have been added since 2007, but I don't think this explains all. Also, concentrating lots of players in one tournament is what matters, in my opinion.)
Poland must be the country with by far the largest number of (skilled) hex players. Until June 2008 (before I knew hex), the Polish server Kurnik aka PlayOK was a breeding ground for strong players. In December 2017, hex was reintroduced, but while it was very active for a few days at least, it gradually died down.
After Poland, the strongest countries would probably be the USA and Canada, based on what I have seen online.
"Hex tournament in Paris" from 2015
The yearly tournaments in France are, I think, tied to Le Salon Culture et Jeux Mathématiques. I don't know if the tournament took place this year. The CIJM was supposed to give an introduction to hex at least, it seems.
See also the HexWiki on hex clubs for more over the board activity. This list might be quite incomplete. But anyway, it doesn't seem like there's a lot.
BoardGameArena(BGA) has more hex players than Little Golem(LG), but LG has more hex specialists.
I'd say the top 5 players active in online hex tournaments in 2023 are Arek Kulczycki, brzytwa, Daniel Sepczuk, lazyplayer and Maciej Celuch. Of these, Arek, Daniel and lazyplayer play on LG but don't play on BGA, to my knowledge. brzytwa plays on both. Maciej Celuch, probably the most prestigious player of all, was last active on LG in 2018, and played a little on BGA recently (won the MSO Grand Prix 2023 • Hex 14x14).
About the future, who knows? Some people and some others (no offense!) put in extraordinary work. Also, the discord server (linked elsewhere in this forum) is quite active, considering it's about hex. I hope the yearly MSO Grand Prix, Mason's monthly hex tournament (sign up for #7 which is on saturday), and BGA's Arena mode will grow (I'm not sure if changing the board size from 11x11 to 14x14 was a step in the right direction though I voted for it), and I hope participation in LG's championships will at least stop falling (will the future ones be double round robin, like the current 11x11 one? That could be bad).