I’ve been looking into travel eSIMs as well and came across globalesim.app that covers most of Europe in the cheapest plan as far as I can tell.
It is not confirmed working on the wiki so far, though. If I read their return policy right, it might be possible to get a refund if you don’t manage to install the eSIM on your FP4.
Confirmed working is yesim, but the offer looks less attractive to me compared to the one above.