Quinn,
You were exactly correct (as usual). SystemPolicyDocumentsFolder was the proper service name for tccutil.
And -- you're also wise to caution us against continual use of tccutil.
But here's what we're facing (mentioned here in case other devs stumble onto this issue): With approximately .5% of our users, we've observed a problem that mostly seems to her with Big Sur, where after the user has granted access, usually by explicitly opening a file (or several() inside a folder that is inside the Documents folder, at some point, usually after a MacOS system or security update, the tcc database gets messed up, and the app's previous permissions are "forgotten". As best we can tell, the Documents checkbox in Files and Folders is STILL CHECKED, but our app can no longer access/open the file we desire. And the user is no longer prompted by the system to grant access. This is in an app that does NOT adopt sandboxing.
I'm going to try the obvious: explicitly present the location of our supporting document template to the user using NSOpenPanel, and see if that will restore access. Normally, the user doesn't ever directly select this file or its enclosing folder. But if that works, great.
Unfortunately, despite discussing this issue with DTS for 10 months, there's been no acknowledgment that there is any issue / defect in MacOS that could cause what I'm seeing. So it MIGHT be pilot error, but hard to see how.