I've worked to get custom XMP fields written to my PNG files, but it doesn't appear that they can be viewed in Photo Mechanic. When pressing "i" I get a lot of IPTC fields.
It would be great to be able to define and/or auto-read these fields, similar to how they just show up in the XnView MP's XMP viewer tab. I'm trying to properly catalog and organize generated art parameters.
I'm not sure whether this functionality exists somehow, but it was asked here in 2019 without a resolution to the thread.