The server is hosted by Hetzner.
I have 50-100 sites (small and large) on the same server, only bitmover's site is under attack. 10+ years on the same contract, several upgrades in the meantime, all this gives me very little room that this bad intention came from there.
I also asked them for a solution to solve this problem and I got a very similar answer as I advised bitmover myself, somewhat more radical settings on cloudflare.
@joker_josue You have well suggested this for a DDoS protection service, I will talk to them about it and whether there are such possibilities.
As far as I can see, most of this bad traffic has been halted so far, CF seems to be doing its job.