Pianos consume some amount of space. That's just a matter of fact with the instrument. A good digital piano in the $600-800 range with proper weighted keys will probably use the same amount of space as a dresser along some wall.

If you seriously want to learn and play piano, even as a hobby, that is the entry level.

I also disagree with using any of the popular apps as anything more than supplemental tools, but there are some very good adult lesson books can definitely form the backbone of your learning. As long as you're aware that posture and technique is a struggle for self-taught pianists, you can look for videos and make some conscious effort to improve at it.

Buying an $80 smaller midi keyboard is a good way to get a cursory feel for things without spending the full amount.

A 49-key will cover 90+% of what you’d want to do in the first year or two of traditional training. A 25-key will get annoying sooner, but if you know space is going to be a real issue, it’s just a percentage question again. You could just decide your skill will be “25-key keyboard” and adapt the training material. But I’d personally consider 49 the realistic minimum to not regularly feel claustrophobic.