I cannot update some applications. Jitsi and Amethyst for some time. Today Syncthing is failing to update. There is a popup with a question to update the app and after confirming nothing happens. After a few tries, there is a message that the package installer keeps failing and asks if I want to quit the app.
I think it might be related to https://github.com/syncthing/syncthing-android/issues/2026 “the next firmware update should fix it for everyone”.
Which app are you using? There are many f-droid clients.
I have noticed that the f-droid downloads sometimes get corrupted. Try redownloading