non-arm-Windows client to Windows host you can use something like parsec where you can adjust resolution on the fly. You can install a fallback virtual display for when the display is off from right inside the app in a single click + UAC prompt. I really don't like parsec though because I know the enshittification will come, and I don't really trust them to be secure or to not abuse their backdoor accesses.

This project allows you to create virtual displays that are persistent, and you can configure them so that when the primary monitor is off the backup one is enabled in windows, just by using the default windows display manager options. You can change the resolution freely... because this is using the same vd driver parsec created https://github.com/nomi-san/parsec-vdd - this works pretty well overall with Sunshine

Ultimately though, Sunshine and Parsec are the only two things i'm aware of with great low latency and high fidelity remote capabilities, aside from niche implementations like what the PS5 has. If something like Xorg had similar quality and latency parity i'd be interested, but i'm under the impression everything is like old school vnc or rdp where it is functional when necessary but not very pleasant overall.