[vbernat]

If you have one screen at 192 dpi, one at 96 dpi, double the resolution of the one at 96 dpi and scale down:

xrandr --dpi 192 --output eDP-1 --auto --output HDMI-1 --left-of e-DP1 --auto --scale 2

I don't have my laptop with me, so I am not 100% sure. You can also go the other way, but the result is more blurry.

Otherwise, as said in another post, apply tips from ArchLinux wiki. I have also put my experience here: https://vincent.bernat.ch/en/blog/2018-4k-hidpi-dual-screen-... (notably if you want something a bit dynamic with a laptop).

[runnerup]

I recommend this, it's exactly how I handle it in Ubuntu at least. I also often use Arandr in addition to xrandr, there's one feature (positioning the tiles if you have a very nonstandard setup) which is way easier to use in Arandr. But Arandr also lacks a lot of options that xrandr has.

You can do it all with xrandr IIRC, but not with Arandr. Arandr just helps with positioning if you have say, three monitors of different sizes which don't line up in any typical way.