staff-see-staff-in-mode option for staff-mode has been removed.
Instead a new permission staff.vanish.see-vanished is added.
Players with this permission can see other vanished players.

Full Changelog:
https://github.com/garagepoort/StaffPlusPlus/blob/master/CHANGELOG-1.16.md

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I will no longer post a release for every mc version on Spigot.
Instead the different versions can be downloaded from https://staffplusplus.org.