When trying to install the Hibiscus banking program, which is only available from the AUR repository, you get an error saying that one or more pgp signatures could not be verified.
Updating the signature keyrings as well as installing base-devel, which was recommended somewhere, did not solve the problem.
The workaround solution is
Install Jameica using either flatpak or AUR. If you choose AUR (Archlinux), then select jdk-openjdk-21 in the installation routine.
Then start jameica and if you are asked, choose your preferred folder for your user data.
In Jameica itself, go to plugins and install the Hibiscus plugin.
Then it works. It took me quite some time to find this simple solution, because once before it worked by simply installing Hibiscus directly through pamac.