For inclusion into their official repo F-Droid requires you to either make sure each build is verifiably reproducible, in which case they will let you sign that

For inclusion into their official repo F-Droid requires you to either make sure each build is verifiably reproducible, in which case they will let you sign that build yourself, or else they need to sign it just like Google will now be doing. They used to always require that they sign it, without offering the exception for reproducible builds. They also support publishing parallel versions with both their signing key and yours, to help with smoother upgrades for users with the app already installed. They do allow you to make your own separate F-Droid binary repo which doesn't restrict your ability to use your own signing key, but then you have to get users to add your repo.