Scale radio control cars/planes/drones

Scale "dollhouse" builds

Swordsmanship.

Whether it's HEMA or otherwise (as long as it's not fencing)

Knife making

Leather working

Classic cars - there is a community https://lemmy.world/c/oldcars@kbin.social but it is basically dead

Learning Scottish Gaidhlig

Aerial arts - silks, trapeze, flying pole, lyra, straps, custom apparatus like cubes/chairs etc. Anything about doing artistic acrobatics on a piece of metal/fabric/other suspended in the air. The community on reddit was the perfect size but pretty much none of them came over to lemmy.

The weather. Be it local weather discussion pages, country etc. especially for big events.

Old Muscle car repair, building, etc.

Individual communities for every car in existence like reddit has. And an active bitcoin community that isn't just a bot mirroring posts from reddit.

Edit: and a community for DJs.

I miss the cursed minecraft communities from reddit(r/phoenixsc and r/minecrafthmmm)

I'd love to see niche communities.

Japanese trains

Roller skating.

r/jailbreak, r/sideloaded, and r/magisk. I moded the first two but there is just not enough activity.

Cryptography

Headphones

How about a community for paracord stuff?

scale models.

Chain mail as both armour and a craft.

Metal, especially progressive metal and music streaming

Pinball