How do I change player gamemode on join?

[Magg]

Hello, this is my first question I ask on this forum and I started recently forge modding.
As the title says how can I change a player's gamemode when it joins the server?
I know it sounds stupid but I honestly couldn't figured out how to do it or where to find on doing it. No youtube tutorials, nothing of use in the forge documentation (this one) and I'm feeling asking if the best choice.

I start with this simple method to register the event, the Player class seem to not have any setGameMode method or anything related to it. However I've found something about a player controller but this mode is intended to be server-side and I'm unsure what to do at this point.

@SubscribeEvent
public void onEvent(EntityJoinLevelEvent event)
{
	Entity entity = event.getEntity();

	if (entity instanceof Player plr)
	{
		// what now?
	}
}

My setup:
Minecraft 1.20.1 (Forge 47.4.0)
Windows with VScode
java version "24.0.1" 2025-04-15

Edited May 31 by Magg
typo

[Magg]

Update. I've figured out, I had to use SeverPlayer class instead.
It doesn't work very well, because in spectator I can still see the health bar but is just a visual bug.

@SubscribeEvent
public void onEvent(EntityJoinLevelEvent event)
{
	Entity entity = event.getEntity();

	if (entity instanceof ServerPlayer plr)
	{
		plr.gameMode.changeGameModeForPlayer(GameType.SPECTATOR);
	}
}