Same issue on our team since about October 11, 2026: every TestFlight build of every app on the team fails with "The requested app is not available or doesn't exist", for two internal testers on two devices. Installs worked on this team in spring 2026. Agreements, tax, banking and compliance are all Active, and builds are Complete and Validated. Filed as FB25219279, and Developer Support case 102995664597. Thanks to anyone on the TestFlight team who can take a look.