Foldable Stationary Bike

This probably doesn’t work here because you mentioned apartment/foldable, but if you have a bicycle you could get a direct drive trainer to put it on.

Something like the Wahoo kicker or similar.

I do a lot of cycling and in the winter I get a Zwift membership for a few months to do some indoor training if its too cold/dark to get out. In the spring I’ll stop paying for the Zwift membership and put the trainer away. I put either my mountain bike or gravel bike on it.