You may not see the same communities, but I have been surprised to see a lot of similar expert types are present here if you can find the right place to ask.
Like I have asked about Linux kernel code regarding the CPU scheduler and gotten good results here too. I miss stuff like Amateur Telescope Making (ATMing), some Maker niches, and people sharing more electronics projects on the grass roots side. Like I etch circuit boards and like to reverse engineer hardware. I like those peripheral projects that popped up and pushed me to get back into a project or start something new. But, I haven't been doing those projects myself and wonder if most of the hobby community has kinda moved on as well.
The only reason I have thought about checking out reddit is for the AI community stuff. There are too many negative people here for the kinds of stuff I play with and no depth of engagement when I do post. There are a few great people, and several researchers but not the hobby like constructive dynamic I need. However I have not visited reddit a single time since June 9th.