Thanks for the help, but still no luck. Using the yay command, the build comes to an end with a signature related error message, no matter if I choose to import the keys or not.
:: PGP keys need importing:
-> B0F4253373F8F6F510D42178520A9993A1C052F8, required by: nginx-rtmp
==> Import? [Y/n] y
:: Importing keys with gpg…
gpg: keyserver receive failed: General error
problem importing keys
This looks pretty much the same as the output of Package Manager, which I was using before.
Maybe it is better to try to import the missing keys. First I’ll check if the missing keys are still valid. If so, I will try to import them.