1 px borders on 4k screens.
Bad contrast which you cannot change because colors are not configurable.
Need to scale my monitor (Windows) because i cannot use custom fonts.
Titlebar cluttered with other GUI elements.
Ribbon using a good amount of vertical space.
Unusable scrollbars - too small/no scroll buttons at end - good luck scrolling through a 500 pages pdf.
Settings resetted with updates.
Automatic updates which change the way the programm works.
And so on and so fort.