Where to put the fitness room?

Good morning!

Does such a room count as living space in the "construction-technical sense," so that, for example, I have to observe the boundary distances?
Is a garage only a garage if there is an actual possibility to drive a car into it?

What I am getting at: building a garage directly on the boundary, without the possibility of access by car, and using it otherwise (e.g., as a sports area) will probably not be feasible, right?

Regards,
Zehn0813

See #5
A garage may not be misused on the boundary nor may a parking space simply be removed.

If you want to train at home, you should plan the space. However, in my opinion, only if it involves regular and long-term use of professional equipment.
It is a hobby/pastime: one plans a fixed PC space, another a greenhouse, and another a gym.
However, if you yourself have doubts about the meaningfulness for residential planning, then the hobby probably has no lasting significance and could also be pursued in a sports center.

If it is important to me to have an additional room, I would build with an architect or, as a standard, use a conservatory as a dining/kitchen area and thus take the gained living space within the building envelope as a pleasant multi-purpose room.