Good DIY projects with limited space/for apartment living?

Look fab labs, hacker space, maker spaces or whatever it is named in your area. Those are not exactly everywhere, but common enough to have a look at. Another somewhat related space would be a repair cafe. That would give you not only access to a workshop, but also a bunch of folks for inspiration.

Other then that look up Arduino and RaspberryPi solar projects. It is pretty easy to find some lists. 3d printers are pretty common, as are many other similar tools. Home automation can also be interesting, but that might not be that great of an option, if you rent. Micromobility can also be somewhat interesting(elector skateboards, self assembling a bicycle....). It is also rather easy to set up a solar system in a flat, as long as you can easily install it outside it on a balcony or whatever. There is also a pretty large diy loudpspeaker community, which apparently is pretty easy to built.

Honestly there are lots of projects. Just think of something you would like to have and look up diy version of it. Seriously people built nearly everything at home. There even was a supersonic kit plane sold once, which apparently never managed to go supersonic and had a habit of killing its pilots, but you get my point.

What are your interests like? Do you want to do engineering-type stuff in your personal time, or not-work-related stuff?

Do you have a separate room from your bedroom, or is it a studio? Some projects are small enough for an apartment, but you don't want to sleep with them (anything involving harsh chemicals or hot plastic).

Do you have space for a dedicated workbench/desk? One thing that really helps with my own projects is having space to leave them out while they're in progress. Having to pack them up and then unpack them again is a real hassle.

Do you have a balcony/patio/outdoor space?

Is money a consideration? Some projects have a high barrier-to-entry (a usable 3D printer will cost several hundred dollars up front).

Possibly most important, do you have any ideas that you want to create but aren't sure how to get there? Projects are most successful when you have a vision for what you want to do, and the skills and tools you pick up along the way are just a means to an end.

Anything metal or wood will probably create too much dust etc.

Maybe get a 3D printer?

You can check on arduino and ESP32 Boards for IoT. That was a hobby of mine, it never took off (albeit, a hobby so it's fine). But I learned a lot about "low level programming" that had no idea it even existed, and there was some interest overlap with self-hosting (home assistant wasn't around at the time, played with Mozilla's mqtt). The latter did took off (I still enjoy doing it).

I'm just getting into bookbinding. It requires surprisingly few tools and not a ton of space (though like all hobbies it can always grow to consume whatever space is available). Its a good option if you have access to a printer with free or cheap prints.

Balcony gardening can be satisfying but might not be what you're looking for.

If you already have a project (or lots of them) in mind, a 3d printer can be great to have around. Depending on your fillaments of choice (determined by what you want the print to be able to do) you might need good ventilation or an enclosure. If you have a spare bedroom that's a good start.

I'm planning to build a solar powered weather station soon - I feel like that's a project I could have done in my old apartment and put out on the balcony.

this dude claims he made a cargo bike on his kitchen table. https://invidious.reallyaweso.me/watch?v=SDlnDEXlfm8&t=56