So, I did some digging, and probably went a little too deep.
It would seem that when the yellow rectangle is shown, the game executable queries for three files: engine\libs\ui\statuswindow.gfx, game\libs\ui\statuswindow.gfx, and finally Game\Libs_UI_4.pak. The first two are not present since they are most likely the original unpakked resource files.
This lead me to take a memory dump of the running Wolcen.exe, and found that some StatusWindow related strings in the dump are located next to the strings 'onButtonNextLeague' and 'onButtonBackLeague'.
This finding prompted me to check back to character creation screen since I had a brief memory of seeing a layout that matches the yellow rectangle positioning.
And 'lo and behold, the league selection screen seems to match perfectly with the yellow rectangles positions.
So, it seems that someone forgot to delete/deactivate the statuswindow drawing/focusing/presence when not in the character creation, or there's some pretty nasty hack to allow switching the league selection using tabulator key.
Fun fact, you can bring up the yellow boxes in the main menu by pressing the tab button several times.