Here’s another issue that Big Sur users may hit: v0.9.1’s volumes() function required all root volume directories to be readable, and would completely crash if any volumes were not readable.
Unfortunately, Big Sur may hide some Time Machine (or other) volumes to users. I’ve addressed this in v1.0.0: (from the release notes):
PhotoStructure could fail to launch if
readdirfailed for any root directories of volumes.