Here is the link to the dev doc: [https://developers.meta.com/horizon/documentation/unreal/unreal-change-display-refresh-rate/]
The part about extended refresh rates is about half way down.
"Meta Quest 3 supports display refresh rates above 120 Hz, up to 240 Hz. This is exclusive to Meta Quest 3. It is not available on Meta Quest 3S, and it is not available on any other headset. Meta Quest 3S uses a different display panel that does not support rates above 120 Hz.
Extended refresh rates require HorizonOS v2.7 or later."
"Up to 207 Hz (standard)
On Meta Quest 3, the display hardware accepts any integer refresh rate from 72 Hz through 207 Hz, and you can request any of them through the standard APIs described above. No additional setup is required. 207 Hz is the highest rate at which the system can deliver a full frame of data to the display at full resolution.
Up to 240 Hz (developer mode)
Rates above 207 Hz require display scaling, because a full-resolution frame exceeds the available bandwidth to the display above 207 Hz. Enable developer mode, then run both of the following commands:
adb shell setprop debug.oculus.forceDisplayScaling 1
adb shell setprop debug.oculus.refreshRate 240
The first command enables display scaling. The frame is rendered at a lower resolution, sent to the display as a smaller payload, and upscaled to the panel’s native resolution by the display hardware. The smaller payload fits within the available bandwidth at 240 Hz.
The second command sets the target refresh rate. Accepts any integer from 72 through 240.
Display scaling trades image quality for bandwidth. The upscaled image is not identical to a natively rendered full-resolution image, and the difference is visible in fine detail such as small text and thin geometry."
