The printer require a lot of maintenance.
IMO you should just use an online 3D printing service.

Take a look at the Prusa Mini and Bambu Lab A1 Mini. It sounds like you want something reliable so I'd stay away from the ultra cheap stuff.

I can't think of any printers that would get smaller if you could slightly disassemble them. They would all take a lot of disassembly, and then still take up almost as much space as before.

I like the idea of just using a print service. More expensive per print, but if you don't print often, it's probably cheaper than buying and maintaining your own.

The library idea is really good, too.

I own an Ender 3 V2 that I use around 10 times a year. It is one of the less sophisticated printers and still it does not require that much maintenance. You have to remove the dust, level the bed and sometimes clean or exchange the nozzle. More sophisticated printers can also do some stuff automatically (e.g. the bed leveling part).

However, the initial assembly and fine tuning took some time (approx. 1-2 hours), so I wouldn't recommend to dis- and reassemble it all the time. If you don't have that much space, maybe check for a small printer.

When I did my research 2 years ago the Prusa Mini was quite popular for small printer. But if you want to print big parts a lot, it might be a bit annoying as you always have to cut them into smaller chunks, print separate and finally glue them together.

How "not use it very often" are we talking about? The critical thing for any printer is first and foremost bed leveling. If you get something like an MP select mini The footprint is about 30cm^3. You can absolutely throw it in a box and just pull it out whenever BUT you will need about 30 minutes to relevel the bed just perfect and potentially run a test print. That said, this machine also only prints a 10cm^3 and it will handle PETG IF it's been modded otherwise it's PLA and that's it.

Which segue nicely into my next question: What will you be printing? Models and minis? Functional parts? Random statues you find online of waifus? (Only slightly kidding)

This matters a LOT.

For the first: The mini will sorta work but not be great with details. Fort the second plan on a printer that can handle PETG at least. For the latter, you want to look into a resin printer. They WILL fit into a closet when emptied and cleaned BUT the cleaning process is both lengthy, tedious and potentially noxious and requires quite a bit of space so I didn't even mention them in the first part.

If you're going to move it, whatever you get, makes sure it has auto bed leveling. Fucking around with that kills the spontaneity every time. I move around an Ender3 V2 with the BLTouch leveler all the time, carrying it with me back and forth from the farm to the city. I plunk it down and it sorts itself out easily.

Stick to a cartesian style though, I have a delta I built and even with bed leveling, it gets out of calibration if I move it.

Idunno why you would want a 3d printer for a print here and there. Most of the fun with 3d printing comes with the printer itself. Hot end gets clogged, bed adhesion problems, levelling problems, diagnosing and going overboard on a simple fix, that what the fun is all about.