Yes thought about this when reading the README. Sidecar has been better than 3rd party apps in this regard (maybe the same technique) but having no DPI control sucks. Thanks for the links, will try to see how it works.
Hmm. Didn't think of that use, but tried it and works nicely. However BetterDummy does not have 4:3 (iPad) aspect ratio support as of 1.0.7, I'll add so SideCar would fill the iPad screen properly.
Thanks, trying it out now! One more thing; can is it possible to have this on Homebrew? Just to make sure it becomes a default app for me.
EDIT: works well with Sidecar -> Mirroring the Dummy display! Lag/latency wise, feels at least the same with native Sidecar. And thanks for the humongous amount of res options, even though I don't need it right now.
I have another usecase: I used to have an off-brand external display that doesn't register HiDPI res to Macs. Bought DisplayResX for that, but maybe this can help. Once again thank you!