More info:
This is a Unity app. If I build it using the standard Unity build system, and I code sign it using the various code sign, ditto, notarization, and staple means, I CAN make it build properly for outside of App Store cases.
But I cannot make a build that the App Store will accept through Transporter. So, assuming my problem could be resolved if I built this through Xcode, I used Unity's option to build and deploy via Xcode.
But the Xcode version gives me the "Invalid Provisioning Profile" error, if I try to push it to the App Store as well.
*meanwhile, another Unity app I'm working on for iOS has been happily building and deploying to the App Store with absolutely no issues, but it's a completely different product, different bundle ID, etc.
"I wish I had never come here, and I don’t want to see no more magic." -- okay I'm not at that point yet. I am happy to try literally anything :)
-Chilton