It is indeed possible for the Creator of a game to promote players to become GMs. Roll20 Wiki said: The Game‘s Creator can hover over a Player‘s icon to manipulate the permissions for that Player .
Promote to GM will grant that Player GM status in the Game, commonly called a co-GM . This is useful for jointly running a Game with someone else or if the Creator would like to become a Player in a Game they created. Promoting someone to GM may also be beneficial in helping another user with GM-level features and or solving Game issues. Promoted to GMs , have limited control over a Game :
Cannot:
Change the next game time display.
Change the Game's description.
Change the Game's settings options, such as the version
of Character Sheet that is set, toggling public access, changing the
background image, toggling character import, or list the game in Looking
for Players.
Delete the entire game.
Kick or Remove Players .
Clear the Chat Archive.
A Co-GM will not have access to the original Game‘s Creator‘s
image library, character journals, handouts, decks, rollable tables,
and other games' pages, however those elements that are being used
within the game are available to the Co-GM. Images that are being used
within the games' pages can be manipulated by the Co-GM as long as they
remain within the game editor. If the Co-GM removes any of these shared
elements they will not be available unless the Game‘s Creator restores them to play.
Can:
Full access to all layers.
Create a new map page.
Put pictures and tokens to the tabletop from their image library.
Assign and edit tokens.
Add handouts, new characters, assign journals.
Move the Players ribbon to different maps.
Play music from the jukebox.
Read GM whispers.
Make macros and token actions and show or hide them from players.
Control dynamic lighting settings if the Game‘s Creator is a Pro or Plus subscriber.
