Cannot open file from iOS Files app via the Open In <My App> share sheet: no file at the provided file URL exists

I fixed this by adjusting some settings in the app's Info.plist.

I switched UISupportsDocumentBrowser to false, and added LSSupportsOpeningDocumentsInPlace, also set to false.

I think these settings were set incorrectly (by me) after I received an email from App Store Connect stating:

Invalid Document Configuration - Document Based Apps should support either the Document Browser (UISupportsDocumentBrowser = YES) or implement Open In Place (LSSupportsOpeningDocumentsInPlace = YES/NO). Visit https://developer.apple.com/document-based-apps/ for more information.