Hi @cobbp
It's the 2.96V directly from the Snapdragon PMIC as you noted, and SD Cards from UHS I and onward negotiate their link speeds and I/O voltage. So, a proper 1.8V SD card will internally use that 2.96V and create the 1.8V I/O rail.
For cards that operate at "3.3V", they are claimed to be supported in the Snapdragon chipsets at this lowered ~3V rail.
The slot on M0062 actually accepts UFS or uSD.
For more details on just the SD portion, please see this design where we opened our Schematics. In this case, this is just uSD, but otherwise matches the M0062 exactly for uSD functionality: https://docs.modalai.com/voxl2-dev-test-board/
Hope this helps!