If you are unable to get your display to support 90hz you really only have two options.
Order an HDMI dummy plug that supports at minimum HDMI 2.0 spec, that way you can add 120hz to it (as long as it advertises 4k 60fps, you can add up to 4k 120hz at 4:2:0 which is what Sunshine and GFE encodes at anyway)
Disable V-Sync and apply a frame limiter at 90fps, this works in nearly all modern games thanks to the new swap chain API which basically allows borderless windowed mode to work like fullscreen mode.
Older games may not allow you to turn off Vsync without first going into fullscreen though
If you have Windows 11 22H2, there is a new feature that allows old games to run on the new swap chain API I believe it is called optimize windowed mode for games.
If you don’t have Windows 11, you can use a third party tool called SpecialK, but it is not very userfriendly and is considered a hack tool, so don’t use against games with anticheat.
Disabling VSYNC works because the way Sunshine and GFE both capture the screen is through the **framebuffer**, not exactly the display itself. So as long as the game is running at 90 frames, you can stream at 90hz on your client without troubles.
There are also several scripts you can install to automate swapping resolutions and screens (if using a dummy plug) here: https://github.com/nonary
If you are unable to get your display to support 90hz you really only have two options.
Disabling VSYNC works because the way Sunshine and GFE both capture the screen is through the **framebuffer**, not exactly the display itself. So as long as the game is running at 90 frames, you can stream at 90hz on your client without troubles.
There are also several scripts you can install to automate swapping resolutions and screens (if using a dummy plug) here: https://github.com/nonary