Since updating to macOS 14 Sonoma, extensions no longer appear in Safari

I have updated my MacBook Air M1 to Sonoma (macOS 14.1) and thus also to Safari 17.1. Since then, all the extensions that I still had under Ventura are simply gone.

But I can't install any new ones either, when I do that, e.g. with 1Password, Evernote or Adblock Pro, the programmes for the extensions just say I should open the extensions in Safari and activate them, but they're just not there.

I have also restarted the Mac in safe mode and restarted Safari several times, but that doesn't change anything.

In Safari Technology Preview Release 183 the extensions are there and work fine. I tried to switch them on and off in Technology Preview, but this doesn't restore them in the normal Safari.

I also tried to remove the extensions from the extensions folder in library and put them back in one by one, but this didn't work either.

I just updated to MacOs Sonoma 14.1.1, this didn't help either.