> tell a non-technical user to set two monitors (e.g. laptop and external) to display text/windows at the same size

Tell me, do you not ever use Macs?

This is not even a solved problem on macOS: there is no solution because the problem doesn't happen in the first place. The OS knows the size and the capabilities of the devices and you tell it with a slider what size of text you find comfortable. The end.

It works out the resolutions and the scaling factors. If the users needs to set that individually per device, if they can even see it, then the UI has failed: it's exposing unnecessary implementation details to users who do not need to know and should not have to care.

_Every_ user of macOS can solve this challenge because the problem is never visible. It's a question of stupidly simple arithmetic that I could do with a pocket calculator in less than a minute, so it should just happen and never show up to the user.