The missing templates_c directory precludes the package from functioning. The original reporter's proposed workaround doesn't properly Debianize the solution, it leaves a directory inside /usr/share that an unprivileged user can write to. It properly belongs in /var/lib/postfixadmin/templates_c.
I have changed the severity to grave since this bug "makes the package in question unusable" as installed, and its unusability is a missing piece and not related to its normal configuration. This should be fixed prior to Debian 11's release or the package removed. Retaining the package will only encourage more users to use improper workarounds that may complicate things when the bug is finally and properly fixed and the user upgrades to the fixed version.
