a comment on the signing key and its usage in debian:
The Taler manual suggests to download
the key https://taler.net/taler-systems.gpg.key
which is in ascii format.
But in apt-key it reads:
"apt-key supports only the binary OpenPGP format [...]. [...]
Binary keyring files intended to be used with any apt version should therefore
always be created with gpg --export."
I tried the non-binary version with
deb [signed-by=/usr/share/keyrings/taler-systems.gpg]
https://deb.taler.net/apt/debian bullseye main
in /etc/apt/sources.list.d/taler.list.
It doesn't work but with the binary version
(created wit gpg --export 0x26E56A5FE7E0266) it does.