… and GitHub lists 6.0 as the latest release 
.
Since you are bringing up F-Droid again … I think it is not so much a version question.
F-Droid only has FOSS Apps, which F-Droid builds itself from the source codes (“It is built and signed by F-Droid, and guaranteed to correspond to this source tarball.”).
F-Droid lagging behind with the version for a certain App may mean F-Droid simply hasn’t built the new release yet … or it could mean the App vendor added something in later versions which is against the FOSS principles of F-Droid. For instance they discontinued offering Firefox, and they don’t have Klar’s brother Focus because of more aggressive tracking in it.
If you use F-Droid for FOSS principles first, stick with F-Droid.
If you just want to have the App whatsoever, stick with whoever offers new versions first .