One way to fix it, but which wouldn't be to the taste of most users very used to GUI programs, is to snap to the nearest width and height of the monospaced font after the user's resize request is completed. It might not be easy to resize the window programatically right after the user forced a resize but... it's just a proposal.
It implies that maximizing the QB64PE IDE window is disallowed, something else that would displease many people.
An alternative is to do what Schism Tracker does but which renders fonts very ugly sometimes. It straight out does a floating-point ratio while drawing glyphs, according to how many rows and columns of text that program thinks there should be, to the total width and height of the graphics screen.
It implies that maximizing the QB64PE IDE window is disallowed, something else that would displease many people.
An alternative is to do what Schism Tracker does but which renders fonts very ugly sometimes. It straight out does a floating-point ratio while drawing glyphs, according to how many rows and columns of text that program thinks there should be, to the total width and height of the graphics screen.