What I can not check now anymore is that reinstalling the archlinux-keyring would probably have fixed this without initializing and populating it. Will try that next time.

If necessary this one

In our example this eventually helped. I remember on my other ssd there was an update of this one. Keep track of this one when updating.
Keep also track of the ‘linux’ package. That is your kernel. Reboot afterwards.

Sources for you to check

https://wiki.archlinux.org/index.php/Pacman/Package_signing#Cannot_import_keys

There you can read this :

There are multiple possible sources of this problem:

  • An outdated archlinux-keyring package.
  • Incorrect date.
  • Your ISP blocked the port used to import PGP keys.
  • Your pacman cache contains copy of unsigned packages from previous attempts.
  • dirmngr is not correctly configured

In addition I found a news post that can also be useful in this situation and other situations regarding the pacman-key.

https://www.archlinux.org/news/gnupg-21-and-the-pacman-keyring/

“In addition, we recommend installing haveged, a daemon that generates system entropy; this speeds up critical operations in cryptographic programs such as gnupg (including the generation of new keyrings).”

For the record I did not do this and everything was speedy enough and haveged.service was not enabled.