I read the correct version for each version with xq, in the package() section of the PKGBUILD. The .SRCINFO shows up without versions, but the resulting package does contain the correct version.

Does the .SRCINFO affect any process of the upgrade? If so, I'll figure out a way to update .SRCINFO with the correct version in the current and future app versions.

The depends makes little sense without a version, please check:

pkgname = nextcloud-app-polls
        depends = nextcloud>=
        depends = nextcloud<

either remove the comparison, or add a version.