I cannot properly view or edit the xcdatamodeld file in XCode12.01 or XCode 12.2 in table view. There appears to be a rectangular white space overlaying the editing area at the top left of the editing area. Because you can see some lines and a bit of the '+' at the bottom of the area.

Yes I have the same issue. Seems OK on my MacBook Pro with Big Sur Beta 6 (20A5364E) and Xcode V12.01, but neither Xcode V12.01 or V12.2 work on my iMac running Big Sur public Beta 9 (20A5384C).