gyrus is unmaintained upstream, and has been archived and made read-only:
<https://gitlab.gnome.org/Archive/gyrus>. Its most recent release was
in 2013.
The version in Debian is effectively a fork, moving it from GTK 2 to
GTK 3. However, there is no Debian maintainer since 2013 either
(see #732011). I don't think it's a good idea for Debian to contain
packages that nobody maintains, either upstream or downstream.
This particular program seems to be a network client, which means it is
probably security-sensitive. I'm also concerned that it's a special-purpose
administrative IMAP client, yet is documented to not support TLS/SSL.
If someone wants to maintain gyrus, I would recommend that they fork the
(abandoned) upstream project and become its new upstream maintainer.
Perhaps this package should be removed from testing/unstable? If anyone
wants it, they can retrieve the most recent version from bullseye.
smcv