Add 120Hz VRR option for displays that have 240Hz, 360Hz, etc.

[waydabber]

Discussed in https://github.com/waydabber/BetterDisplay/discussions/4402

^{Originally posted by portral June 3, 2025} I'm not sure how feasible this is, but for external displays that have higher refresh options, it'd be nice to have intermediate VRRs if possible, I .e. a 4K 240Hz display could do 120Hz, a 360Hz could do 240Hz or even 120Hz, etc.

I'm not sure how feasible or easy it would be to do, but it might help with some of the VRR issues macOS has with flickering and such, depending on the software or content being used, etc.

[waydabber]

@portral - yes, this would indeed be an useful feature. You can do so right now with an EDID override, but adding a simpler UI for such features is certainly possible.

Also, the adaptive-sync-limits override parameter might work, like this:

	<key>adaptive-sync-limits</key>
	<dict>
		<key>allowed</key>
		<true/>
		<key>max-rate</key>
		<real>120.0</real>
		<key>min-rate</key>
		<real>48.0</real>
		<key>max-frame-duration-increase</key>
		<real>3.0</real>
		<key>max-frame-duration-decrease</key>
		<real>3.0</real>
	</dict>

You can use the max and min rates as hard limits and frame-duration values to control jumps between frames upwards and downwards which might help reduce flickering.

[RdWing]

I have been using EDID overrides to do this, helps to squeeze certain bandwidth-limited monitor connections to the max haha. If it's possible, I would love to see this feature. Wonder how it interacts with ProMotion.