Pretty sure VRR is a mode as far as the display (controller) is concerned.
There’s very likely still a scan out rate determined by the maximum refresh rate, just that the source can delay the next frame if it’s not ready yet.
In other words, e.g. 120 Hz and 144 Hz of VRR aren’t the same even when displaying a 60 Hz signal at the moment – the faster signal would have more pauses and a higher signal rate.
As far as I understand it, nothing "clocks down"; rather, frames are delayed as required to achieve the frame rate desired (or reachable, in the case of gaming) by the source, down to 1 Hz.
So, yes, fixed 120 Hz and 120 Hz with VRR and without any skipped frames might well be the same mode to a GPU, but it also might be a different one, requiring a mode switch. I don't know how Apple has implemented it.
But in any case, for the bug at hand it's irrelevant: Apple's ProMotion uses a refresh rate of 120 Hz, so switching between that and 60 Hz is definitely a mode switch.
There’s very likely still a scan out rate determined by the maximum refresh rate, just that the source can delay the next frame if it’s not ready yet.
In other words, e.g. 120 Hz and 144 Hz of VRR aren’t the same even when displaying a 60 Hz signal at the moment – the faster signal would have more pauses and a higher signal rate.