Updated this post to revise the question being asked. Where can one see the Release info for the version of groupfolders being deployed to NextCloud v18? (groupfolders is at v8.1.0 for NC20, but 6.0.8 for NC18)
You may see different version numbers for the GroupFolders app, comparing what shows in Github, vs what comes up in an installed application.
In Github lastest version is v8.1.0
But via admin interface in a production installation you may see a different version number for GroupFolders if you are on major release version of NextCloud eg v18 or v19
See this page in the NextCloud App store (screenshot below)
Scrolling down this includes a table which lists which version of GroupFolders which goes with which NC version.
That helps one understand what goes with what.
Remaining question then relates to updates to the versions of groupfolders deployed to older versions of NextCloud. So for instance, for NC18 the groupfolders app has just gone from v6.0.7 to v6.0.8. Where in github can one see what went into this release of groupfolders?