I don't run a compositor, and with Qt6, Some programs like VirtualBox just don't respect Qt's scaling factor setting. Setting the font DPI instead results in weird bugs, like the display window getting smaller and smaller.

As it happens, VirtualBox does have its own scaling setting, but it's pretty bad, in my opinion. But I'm kind of forced to use it because Qt's own scaling just doesn't work in this case.

That's great, however why do we use a "scale factor" in the first place? We had a perfectly fitting metric in DPI, why can't I set the desired DPI for every monitor, but instead need to calculate some arbitrary scale factor?

I'm generally a strong wayland proponent and believe it's a big step forward over X in many ways, but some decisions just make me scratch my head.

Seems like the support is getting there. I just checked Firefox and it has landed the code but still has it disabled by default. Most users that set 1.5x on their session are probably still getting needless scaling but hopefully that won't last too long.