I didn't really plan to build HCI as a hobby, but I have a strong interest in hardware engineering and eventually I wanted to switch back to building things that anyone can physically see.
Years ago I built a hemisphere keyboard and now I've built an LED globe with a viewing portal. I started building visible things again because I had a vision and it's very satisfying to use the result. I spend more time using it now than I did originally building it, although it is definitely a work in progress. I want to build it again for a 2.0 version.
You have to accept that 5-15% of the people who would show up to something like this are genuine weirdos you probably don't want to be around. And another 10% at any given meetup are autistic or neuro-divergent but well-meaning, kind and full of interesting insights and hobbies, although perhaps difficult to socialize with, at least until they get to know you're well-meaning too.
These challenges come with the territory. You end up talking to people you'd otherwise never meet in the normal course of your life, and it's neutral at worst and wonderful at best.
Do you have any interest in digital humanities? Knowledge work where verification is still important but not as black-and-white as does the math check out, does the code run.
Do you have any interest in family history or genealogy?
https://vibegenealogy.ai/p/the-genealogical-research-assista...
Recommendation -- don't stall the glider at heights between 10 and 25 feet from the ground. Also, avoid barbed wire fences.
I play chess but not chessboxing but hey, you asked for some interesting niche hobbies!
It seems that what you do is mostly related to computers within the niche hobbies but what if you can do something else too?
> Right now I'm making a chess engine, but that's already a solved problem
Not everything should be done for the end-result, sometimes its the process which matters, there was a great hackernews post about it (https://ergosphere.blog/posts/the-machines-are-fine/)
If you want something niche, perhaps make some portal-2 mods or make more efficient versions of using GlaDOS TTS within browser etc. (this is just something that I want to be honest, but I feel like it can be a niche hobby in its regards seeing your interests)
Let me know if you want more ideas and have fun and have a nice day man!