Works as expected in 1.20.2, but not in 24w12. Haven't testing versions between those two.

Was put into skybox on Blue team. Clicked the button to join Red team. Did not get the usual chat message, nor did I actually change team. When first item was found, I was still shown as being on Blue team.

Not just the Red team button either. None of them work.

Looks like the advancement for detecting button presses is broken, and I can't figure out how to fix it.

You can run /tag @a add fetchr.pressed_button to just permanently give you the tag in the snapshot. In multiplayer, this will cause the wrong person to get added to the team, when a player is closer to the button then the one who was pressing it, though.

It does work correctly in 1.20.4 and below.

Looks like it's a MInecraft bug, waiting for https://bugs.mojang.com/browse/MC-270175 to be resolved.

If that doesn't get resolved in a timely manner, an alternative would presumably be signs that trigger a team join function that uses @s to reference the player.

I'm not gonna use signs they are ugly and obscure the team color. I'd rather fake a button press with interaction entities and a playsound. But I am positive they'll fix it

Confirmed working in 5.1.2-rc1 on 1.20.5-pre1