Hi foolproofer, I've the same problem here in Germany with a german keyboard. As long as QB64 is setup to use CP437 with the inbuilt standard font, typing the german umlauts (ä,ö,ü,ß) gives wrong results on the display. Also some chars which are reached via the AltGr key on my german keyboard (µ,€,²,³) give wrong results. However, if I save the text in QB64 and then open it in the Windows Editor or Notepad++, then the wrong chars magically got right. This is because Editor/Notepad++ are using windows CP1252 (Western European).
If you switch QB64 to the correct Windows CP for your country and also use a unicode custom font, then it should work. However this affects the IDE only, in your programs you have to use a _MAPUNICODE table with a unicode custom font to achieve the same.
Of course it would be nice, if the whole thing would work with the CP437/standard font setup too, especially because it was already working in the old SDL versions of QB64.
OpenGL seems to do some kind of pre-mapping keyboard inputs to the active system codepage before it hands over the inputs to QB64, which then leads to wrong results on CP437. Something must have been different here in SDL. However, as the majority of QB64 users is sitting in the US were everything is working just fine, I doubt that anything about that issue will change soon (waiting since 6 years).