Toilet too close to the wall, what now?

Only possible if you tear the wall back to the shell construction. Different built-in frames, different water pipes, different sewage pipes – nothing big fits through with the bidet ;-)

Of course, you have to extend or replace the pipes. My plumber finishes that in an hour with drywall.

The damage is indeed done and final. €150 pain and suffering as tuition fee. It will be better with the next house.

Nonsense, there are completely different "construction sites" that would really be problematic. A few tiles and 3 pipes newly laid are usually no rocket science.

Nonsense, there are completely different "issues" that would really be problematic. Relaying a few tiles and three pipes is usually no big deal.

Not problematic. But really EVERYTHING has to be redone (truly complete dismantling including replacement of the flush-mounted frames). That’s not something done "just like that." It takes a lot of time and money.
You can take another look at the photo from the shell construction phase.

Distances and movement areas for sanitary fixtures are regulated in VDI 6000. To my knowledge, the 20cm to the wall is also mentioned there. Common distances are 40-50cm from the wall to the center of the cistern, depending on the available space.

A different question of belief.... Do you really need a budget ???? Or get rid of it and just put the toilet in the middle

Just a different matter of faith.... Do you really need a Bidget???

Those who don't have one simply can't judge - those who have one and use it properly will never give it up. Also saves detergent in the washing machine...

Those who don't have one simply can't judge - those who have one and use it properly will never give it up. It also saves detergent in the washing machine...

Shouldn't one be able to wipe one's bottom well enough without a bidet so that no more laundry detergent is needed for the underwear?
A bidet is a nice thing, but there is also moist toilet paper.