This seems to be the same issue / root cause as MCL-17721. I can confirm the effect on Launcher 2.2.2528, UI 7293 on Linux/Debian.
This is affecting all dropdowns in the launcher (for example on the top left Mojang Account dropdown, inside account management, skin management). It seems that the open dropdowns do accept Mouse Move/Hover events (the selection changes), but the Mouse Click is handled by the layer below – the effect is like clicking besides the dropdown item. Anyway it seems to be just an event handling / routing issue on the UI.
Workaround: You can operate all the dropdown items with the keyboard (arrow keys up/down + return/enter) without problems, even if you hover with the mouse and press enter instead of clicking.
Same behaviour in 2.2.3963 / UI 7473 @ Linux/Debian.