I cannot reproduce this.
Default TAdvStringGrid on the form and initialized with
grid.RandomFill(false);
Default font is correct.
Changed font size at design time to 9 and remains correct
Changed font size at design time to 9 and remains correct
Tested with font size change at runtime to 9 and remains correct
Tests performed here on 4K monitor with Delphi 10.3.1 Rio with default project settings (per monitor high dpi)
So, I can only guess you are doing something different and details are missing to allow to reproduce.
Tests performed here on 4K monitor with Delphi 10.3.1 Rio with default project settings (per monitor high dpi)
So, I can only guess you are doing something different and details are missing to allow to reproduce.