when in a state of logging in you can use the creative menu

[ArtOfLuxis]

when in a state of logging in you can use the creative menu if you were in creative before logging off

this doesnt do anything bad in vanilla, but some plugins may have items that dont need interacting with to use them, so cancelling the event won't do anything

[ArtOfLuxis]

you can add the "force-spectator" option in the config for servers with plugins like these