Hi,
Sorry to hear you are having problems getting previews working.
Crash logs for the preview app will show up in ~/Library/Logs/DiagnosticReports/. It can sometimes take a few minutes for it to generate, so give it a bit time and then see if any are there. Hopefully that will give you some helpful hints on what is causing the crash.
Based upon your description of the situation I am guessing that the preview version of the app has some stale app data (perhaps an old version of a CoreData container that doesn't have migration support to the current version?). To start from a fresh slate you can use the terminal app and run xcrun simctl --set previews delete all.
If that still doesn't resolve issue then probably best next step will be to file a feedback with diagnostics.
We will need the diagnostics Xcode Previews generates in order to make sure we understand the error the previews system is encountering.
If you are having issues with macOS, catalyst or on-device iOS previews then download and install the logging profile for your device. Instructions and profiles are available here: https://developer.apple.com/bug-reporting/profiles-and-logs/?name=swift
Attach the sysdiagnose to the bug report as well as the diagnostics using the instructions below.
Then when you get an error in Xcode Previews, an error banner appears in the canvas
- Click the "Diagnostics" button in that banner (or if the banner is missing you can use the menu: Editor > Canvas > Diagnostics)
- In the sheet that appears, click "Generate Report" in the bottom left of the sheet
- Attach (or make from the folder) the resulting zip file to the bug (will be named something like
previews-diagnostics-0123456789.zip)
