I'm having similar problems with Xcode 13beta 1 on Intel MacBook Pro even after rebooting.But latest regular MacOS 11.4. It just crashes on launch. it somehow appears to have corrupted Quicktime which can no longer play files which played a day or two ago(QT gives could not be opened, unknown error(-101).I can Airdrop and play the same files on iMac. Tried AirDropping Quicktime player from iMac(same OS and similar hardware) to MacBook but still couldn't open file so it looks like some QT subsystem is corrupted. Have also lost sound playing YouTube vids in Safari. Mail messages containing videos are also showing files as unplayable on MacBook (quicklook? preview in Mail shows black background with play icon with line through it. Vid in same email shows normally and plays on iMac. I know Paul Hudson was having audio problems on his Mac after installing this beta

Same problem with nil TabController even after trashing and reinstalling Xcode from App Store - Version: 12.3 (17715). but crashing without opening anything, Solution was to open a random single file(it was a swift file but probably not significant) It crashed, Reopened it and, while Xcode was loading, I was able to get to File/Open Recent/Clear Menu... and cleared it and was then ok. I assume there was some corruption in the default previous project that it was opening (but I couldn't figure out which that might be . Couldn't find any xcodeproject or similar file mentioned in the crash or system logs A previous attempt to Quit Xcode failed presenting a Cloning GitHub project dialog that was hung and wouldn't cancel so had had to Force Quit it, presumably corrupting some file. Seems like Xcode should recognize repeated failures to launch without user interaction and offer to ignore opening the default/previous project