Close button does not close the game, instead shows a gray screen

I launched Minecraft 21w05a from MultiMC, then I created a new world, pressed F3, opened chat, typed "/tell " and clicked the close button.

A gray screen appeared, as visible here:

I waited 13 minutes, but nothing happened. Then I killed it.

[https://gist.github.com/kb-1000/c53ea7c1be55d38be42f06e87a1489db