Most of the functionality (except sha1_transform) of Digest::SHA1 is also provided by Digest::SHA. Switching from Digest::SHA1 to Digest::SHA should be in principle as easy as substituting the use of Digest::SHA1 with Digest::SHA.
Digest::SHA is in Perl core since version 5.9.3 and thus is in Debian’s perl since Lenny.
Changing use of Digest::SHA1 to Digest::SHA would thus reduce external dependencies by one.
Packages using Digest::SHA instead of Digest::SHA1 can then drop the (Build-)Depends(-Indep) on libdigest-sha1-perl.
I posted all of the fixes to the script with my nickname by the fixes in an echo and gave info why.
Look at the script update proposal for Debian 12 thread contains a boat load of info.
There may be some things I’m missing or even a better way to handle things but never the less it is what I will resort to using personally to resolve a lot of the issues at the moment.