Hi, this issue has been raised many times in reddit and other forums. Support for hidpi (e.g. my screen is 3000x2000) is rather deficient. Buttons, checkboxes and other widgets look minuscule. The decorations in the Fringe are barely visible. I'm not sure whether the best strategy is to offer manually scaled up pixmap variants or to automatically scale them up even if the result ends up being a bit blurry. In any case, most screens in sell today are mid or hi resolution, it's almost impossible to buy a decent piece of new hardware with a good old 1366x768 screen. And emacs should catchup.
I propose to make an inventory of all the things that should be fixed towards hidpi support and maybe provide an external package patching whatever could be patched as a temporary measure.
I'm using emacs 26.3 in Ubuntu 19.04. My DE is Gnome 3.32, scaling factor = 2.
Best regards
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Carlos