When I load a package that is installed with a prerelease version, the version object is null because does not allow prerelease.
If I check te msdb.dbo.sysdac_instances database the installed version is set correctly with the prerelease version.

using var dacpacPackage = DacPackage.Load(dacpacFile);
dacpacPackage.Version

Accessing Metadata by reflection can access the right version
I think the public Version property needs to be changed to use some structure that allows prerelease/Semver versions