Here is what the good folks at Tier Im Recht Foundation, a group that are experts on Swiss animal law, have to say:
https://www.tierimrecht.org/de/recht...ck-hinterlsst/
Translation courtesy of Deepl, because my little grey cells have already had enough exercise today
If a cat causes damage on a foreign property, the damaged neighbour may have to pay for it himself. In most cases the owner is liable for the damages caused by his animal, but he can still not be held responsible in every case. You can find more information about the so-called pet owner liability, here.
(My note - follow the link in the German text, it's a general statement on liability wrt pet ownership. )
TIR then continues:
A cat owner - unlike a dog owner - cannot be expected to constantly supervise his animals. For this reason, he does not necessarily have to take responsibility for damages caused by a cat on a foreign property. But he is liable at least if he has already been legally obliged to prevent his Büsi from entering other people's property and apartments and still has not taken the necessary precautions.
---
Damage caused by a free roaming cat is a tricky one in law, as cats are considered by nature 'semi-wild'.
So first step, talk to the cat owner. Try to find a solution together, emphasizing preventing future visits. Ask him what he might suggest to deter his cat. Toss in a comment about the damage - hopefully if he has any moral sense he'll voluntarily offer to pay for cleaning.
However, be prepared that some cat owners will shrug off any responsibility.
If that happens, your choice is to either resign yourself to paying for the damage or to try to take the matter further - but be aware that the latter is likely to cost you more than it might be worth.
So... that's a bit about the legal situation.
Were it me, I'd focus on looking for common ground with the owner and finding a practical solution to deter visits. And for that, I'll defer to the forum cat experts.