List more in the comments! I'll add them if they are a community for a video game genre, and have had at least one post in the last month. Crossposted to !games@lemmy.world here.

• !adventuregames@lemm.ee (also has puzzle and interactive fiction)
• !arcaderacing@lemm.ee
• !automationgames@lemmy.zip (replaces dead feddit.de community)
• !citybuilders@sh.itjust.works
• !cozygames@lemmy.world (replaces dead feddit.de community)
• !crpg@lemmy.world
• !dailygames@lemmy.zip (for quick once-a-day web games like Wordle)
• !fgc@lemmy.dbzer0.com and !fgc@lemmy.world
• !incremental_games@incremental.social (having federation troubles, but as someone with an incremental.social account I can guarantee we are active)
• !jrpg@lemmy.zip and !jrpg@lemmy.world
• !lifesimulation@lemmy.world
• !metroidvanias@infosec.pub
• !otomegames@ani.social
• !rhythmgames@lemm.ee
• !roguelikes@lemmy.world
• !shmups@lemmus.org
• !simrallyracing@lemmy.world and !simracing@lemmy.zip
• !soulslike@lemmy.zip
• !strategy@lemmy.world, !strategygames@sopuli.xyz, !turnbasedstrategy@lemmy.world, !turn_based_tactics@lemmy.zip
• !tycoon@lemmy.world
• !visualnovels@ani.social

I also found some genres with dead communities. Maybe someone would like to revive one, or make a new one (preferably on a smaller instance than lemmy.world)?

• !horrorgaming@lemmy.world
• !platformer_games@sh.itjust.works
• !puzzlegames@lemm.ee (yes, !adventuregames has some, whether puzzles actually belong with adventure games is another conversation. I don't think so but I'm not an expert on either genre)
• !realtimestrategy@lemmy.world and !rts@reddthat.com
• !survivalgames@lemm.ee

On my search for communities to put here I found some genres seem to be wholly missing. Let me know if I missed something!

• MMOs
• open world/sandbox
• RPGs that don't really fit in CRPG or JRPG
• shooters (think FPS, hero shooters, literally any shooting game that does not fit in the shmup/shoot-em-up genre)
• simulation in general
• sports
• stealth