Ok, you clearly don't know what F-Droid is.

F-Droid builds all apps by themselves, which especially with their old servers took a lot (between detecting that the update exists, building the app and going to sign everything at their air-gapped signing computer).

Now a lot of apps use the "reproducible builds" feature, which means that F-Droid will distribuite them as they come from the author, leaving their digital signature; but they still need to build those apps before distributing them, to verify that what the author built corresponds to the declared source code.

With the much powerful servers that they've had for a few months builds are a lot quicker, but there are still steps that can take several days, especially the part of signing the apps' index on their air-gapped computer.

There's a ton of things that could be improved, and it would be best if there were an alternative with better maintainers, but they're currently the only service of this kind for Android (well, IzzyOnDroid is a partial alternative, if you're careful to check their reproducible builds results).