Yes, they manually sign every package.

But they could easily have their own F-Droid repository, I have repositories for FUTO apps like Grayjay and their keyboard, Bitwarden, and Newpipe, among others. Those are run by the projects themselves, so they’re in charge of how often they update it, as well as how they sign it. So if they have issues with the “official” F-Droid repositories, they can always host their own. I honestly prefer projects that host their own repos precisely because they should, in theory, update faster.