When LuckPerms is installed, BuildSystem adds extra contexts
build-mode
Whether the player is in build-mode (/build)
/build
true, false
true
false
role
The player's role in the current world
creator, builder, guest
creator
builder
guest
You want players who are guests in a world (neither creator nor builder) to remain in the gamemode they currently are in.
Now you can use the following context: /lp user <user> permission set buildsystem.gamemode false buildsystem:role=guest
/lp user <user> permission set buildsystem.gamemode false buildsystem:role=guest