I updated Photoshop and Adobe Camera Raw yesterday to the newly released PS V23.0 and ACR v14.0.
It appears that the new masking features (especially select subject/sky) now create a 2nd side car file containing editing data.
In addition to creating or adding to the <filename base>.xmp file, ACR now appears to create a <filename base>.acr file (it appears to be a binary file). I suspect this contains data associated with the new select subject and select sky functionality
Photo Mechanic (I'm using Photo Mechanic Version 6.0, build 6097 (85d1687)) does not appear to recognize the file as a sidecar in at least two ways:
1) The .acr sidecar shows up as a separately listed file in the contact sheet, and
2) When I copied the file (File menu Copy/Move Photos...), PM copied the raw and .xmp file but not the .acr.
As a work-around, we can either copy/move the .acr by hand and it looks like ACR (and probably Lightroom, but I've not tested it) might be able to recover the masks by rebuilding them, but it would certainly be better if PM could copy/move all 3 files together.
Thanks,
Don