Two screens with different resolutions

You can scale screens independently from built in settings:

settings -> devices -> screen display

Click on the monitor you want to change then choose appropriate scale.

If you need more customization you could use xrandr (built in configuration utility to the RandR (Resize and Rotate) X Window System extension). it does affect the resolution though.

use xrandr | grep 'connected' to find active displays, identify which monitor you wish to change. The part you're after is the characters on a new line before the first space.

for me: eDP-1

Then you can use xrandr --output eDP-1 --scale 0.5x0.5

Edit: Then you can use xrandr --output eDP-1 --scale 2x2 to zoom out (0.5x0.5 zooms in)

For more indepth use of xrandr scaling without the negative side effects you could try reading this blog. Looks legit, but not tested.