Toolkits like Qt and Gtk only support integer scale factors. (Qt does fractional, but still has glitches) The scaling factor in the article inside gnome tweaks only changes the font scale. I personally use 2x Gtk scale and 80% font scale, and it works OK, but it’s not perfect.

Gnome has a feature in Wayland (Ubuntu has a third-party patch for X11) that scales up to an integer ratio then scales the image back down to fit the right size by making the display frame buffer larger. This is what Mac OS does. It’s slower here than on Mac OS, so it’s not very optimized, and it leaves things ever so slightly less sharp.

I think it really depends on what programs you use.

I pretty much only use Firefox and terminals. So I set ~/.Xresources Xft.dpi to something that looked nice. Presumably a bunch of programs ignore this (otherwise I wouldn't be seeing complaints about HiDPI online).