You could give 7zip [1] a try. According to [2], 7zz integration does not need code changes. You'd have to deploy 7zz manually, though, as I don't see it in EPEL either.RPM names are p7zip and p7zip-plugins on EPEL for Centos 8.
p7zip and p7zip-plugins do not provide 7zz, but 7z and 7za. Per Nikolaos' given @decoders, Amavis tried 7z and failed.
