My lower res, lower DPI display from my old Dell laptop looks much more sharp and crisp than the fancy pants Framework 13 high res display.
No, electron, xwayland, GNOME cause problems.
KDE with fractional scaling on Wayland works well.
Not sure about GNOME today, but they hid it away in the past and forcing 120%/150% made everything blurry
Meanwhile, macOS has been handling high-dpi displays with zero issues since 2012.
This is just a theory but I assume they just dont scale, they have their UI sized to a set size and thats it.
You assume incorrectly.
The way it works on macOS is that you select the ‘looks like’ resolution to determine the size. For example if you have a 4k monitor you can set a ‘looks like’ resolution of 2560x1440. Internally it always renders at 2x, so in this case it will render to 5120x2880. That image is then scaled down to the actual display resolution, e.g. 3480x2160. It’s basically supersampling.
