Summary:
When Minecraft is launched from the NEW launcher, trying to resize the window makes the GUI glitch out.
NOTE:
It has to do with redrawing: When placing the mouse over a button (at the location it should be normally), it will highlight!
NOTE 2:
This affects ALL MC versions: I tested a version (before the new launcher) I used last without problems, this time the bug
Screenshot 1 - Happens when scaling down
Screenshot 2 - Happens when scaling up
There is a way to refesh it:
Click out of the window (as to make it unfocussed) and then click back in. After a couple of seconds, it will redraw correcly
I confirmed this only happens in the new launcher:
Downloaded the latest older version (Bootstrap v5) and launched the save MC version -> Resize works
Also when modding in Eclipse, the version launched from Eclipse resizes seemlessly
Cannot reproduce, does this still occur for you in the latest launcher version? if so, please use the Mojang Support Center.