I just caught this bug this morning with Xcode 26 beta 6. I promptly filed feedback with a sample project. FB19931677

I just started experiencing this with Xcode 12.2b2. I can view and edit models using the graphical editor, but not the table based editor. I tried to use VoiceOver to see if it was a dialog that could be dismissed, but I had no luck. I didn't have any luck even falling back to Xcode 12.0 (12A7209).