I was deploying my apps to my device fine until I upgraded to iOS 15 public beta 3 and XCode 13 beta 3. Now it shows the message "Untrusted Developer: Your device management settings do not allow using apps from developer ...". I don't find anything in Settings > General > VPN & Device Management where I can press trust for the app. I've deleted the provisioning profiles in XCode but that didn't help. Can you deploy apps to a device with beta software on an unpaid developer account?
The solution is to create a new Apple Developer account. In XCode go to Signing & Capabilities, in the team drop-down select "Add an account..." and sign into your new account. Press Run in XCode. It will come up with the same message but go to Settings > General > VPN & Device Management and trust the app under "Developer App". This didn't appear before.