The SMP Spectator plugin [https://www.spigotmc.org/resources/smp-spectator-mode-1-16-support.77267/] needs an update to a newer version as the currently available version is bugged. The permissions don't work.
This bug is not present on new versions of the plugin as seen here: https://www.spigotmc.org/resources/smp-spectator-mode-1-16-support.77267/update?update=377087.