Thank you very much ! It also works for me and my Fairphone 4 is easily usable now :-). But as Fabian3 said, I thonk it would be better to have an update from Fairphone, or to extend the community of “beta-testors” in order to cover a wide range of possible bugs.
The only remaining strange thing is that when I swipe down on my screen, the “Wallet” icon is now always on and I can’t turn it off. This wasn’t the case before the Android 15 update. I hope this won’t be a source of future problems…