My setup is a 2021 MBP 16" connected to a 3440x1440p monitor at 144Hz via DisplayPort.
/System/Library/Displays/Contents/Resources/Overrides/ was the solution on Intel/AMD macs but it doesn't work on Apple Silicon.
BetterDummy is the only workaround I could find but it doesn't support any refresh rate other than 60Hz.and also looks rather blurry compared to "native" HiDPI.
I cannot disable SIP as this is a work-provided machine. I do have root privileges though.