Welcome to the forum, Johannes!
The odds of an operator officially supporting FP4 seem to be relatively small from my experience - simply because the FP4 is a relatively rare device.
eSIM is sort of a standard, however. So even without official support it should work “in most cases”. The difference is that nobody will really want to guarantee that. So in the end you’ll just have to try, unfortunately.
Some people already use eSIM - including myself - and in general it seems to work as far as I can tell. In my case I’m using Congstar in Germany without any trouble.
But there are also exceptions like this:
If you search the forum for “esim fp4” or similar, you can find some additional examples of what works and what doesn’t.
PS: If you decide to try it with your current operator or somewhere else, then please report back so others can learn from it.