.deb package uninstallable on Debian 11 Bullseye

[ghost]

Really just an FYI as I don't know if it's easily fixed. Debian 11 removed package "libappindicator3-1" so Petmate's .deb is no longer installable; results in following error:

# apt-get install libappindicator3-1
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Package libappindicator3-1 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'libappindicator3-1' has no installation candidate
#

According to element-hq/element-web#16174 (comment) for a different package, "libayatana-appindicator" could be used. However, it seems it would need to be done in the code as merely installing "libayatana-appindicator" does not resolve the .deb install issue.