v4.0.0RC1 (not v4.0.0) is the newest version in public-repo & package manager
The eXist public-repo and dashboard package manager are showing 4.0.0RC1 as the newest version of TEI Publisher.
This is because "4.0.0RC1" is not a valid semver string, so the public-repo's comparison is essentially unable to distinguish between "4.0.0" and "4.0.0RC1". (The relevant portion of the public-repo's version parsing code is: https://github.com/eXist-db/public-repo/blob/master/modules/scan.xql#L20-L24.)
(The public repo should really reject invalid semver - but it doesn't.)
The solution I'd recommend is to fix the version number so that it is a valid semver string, "4.0.0-RC1" (with a hyphen between "4.0.0" and "RC1").