Since I installed the Fossify phone app (it’s layout suited me better) I cannot accept phone calls, i.e. the green button gives no reaction, whether I (try to) push it or move it.
The pre-installed app works fine.
Perhaps try
Settings > Apps > Fossify phone > Storage and cache > Clear storage.
This will have the same effect as uninstall and reinstall and give a fresh start.
Emptying storage/cache didn’t help. I stick to the original one, apart from the layout it’s OK.