Slanted walls - distance of baseboards

It's the same with us. I was advised against acrylic, etc., because only lint sticks to it or it cracks. I'll leave it as is and be done.

I am also critical of acrylic. It looks good at first, but it attracts dirt and it is difficult to remove/wipe off. At least that is our experience.

Let's put it this way, if you had wanted a 99% flat wall, you would have had to pay more. The deviations are within the range of normal tolerances.

Which tolerances apply here, or which set of rules should one look at?

A flat wall exists (only) artificially through these drywall panels or whatever they are called. Plastering is a craft, there are different quality levels, Q1-Q4. It is about how precisely the plaster is smoothed. It will never be 100% even anyway. Anyone who has never dealt with crafts, that is, what characteristics a craftwork has, should do so. In life, you don’t only deal with factory-made goods. Baseboards = factory-made goods, house plaster = craft. I see you have textured wallpaper: then the next question is already lurking: are the cracks between the wall and ceiling normal or how much are the defects worth? This is also quite normal when cracks or joints between two materials crack because they move. Since they are connected with paper (textured wallpaper), it also tears.

Which tolerances count here or which set of rules should one look at?

This must be polished off. Otherwise, acrylic yellows and attracts lint.