This sounds like a very weird edge case and it's very easy to say this sort of statement in retrospect, but I wonder what percentage of engineers would think of testing this specific combo beforehand.
As someone who works on embedded devices with a lot of experience with Hardware-in-the-loop testing, this is 100% a QA oversight.
The way this feature is implemented screams "test it from boot to reboot". I wouldn't pick too much on a small company doing some basic BSP/application work for some HMI device or something like that, but this is the richest company in the world with major funds/infrastructure to be better than this.
Do we have info about the implementation somewhere?
It's a single setting prior to a standard update. Now I'm not saying they should test every combination of settings, or even every individual setting. I'm more curious how there is any interplay between this setting and the update, and why that has any effect. On the surface it smells like a system design issue to me - like something is going in there on that shouldn't be.
There is (probably) a logic behind it.
https://mstdn.social/@marcan@treehouse.systems/1113296141101...
> Why [does disabling ProMotion cause this problem]? I can tell you why: because Apple hates display modeset flicker, and switching modes between ProMotion on/off causes a modeset flicker, so of course they made it so that is stored in nvram somewhere and applied when the screen is turned on during early boot, so when macOS boots it doesn't have to flicker again.
I personally appreciate how Apple prioritizes these little details—and I'd argue it's a huge part of what has made the company successful. This is the company that put a speaker in the iPod just to have a clicking sound for the scroll wheel.
For context, I hate it when the built-in display is not consistent with my external displays.
Few displays actually support ProMotion rates. So chances are that if you use any external display, you’ll have this jarring asymmetry. So you’ll want to set your rates manually.
Using an external display with your MBP doesn’t seem like a weird edge case to me.
On the other hand, Apple has problems with the M series chips and high refresh rate mode timings on external displays, so you're technically correct about the compatibility.