Not an answer as such: I have the same issue — under Catalina as well as Big Sur — but I see that it has been fixed in Monterey. Try your code under the Monterey dev beta.

Better panel example:

Hi, Ziqiao I did file report (FB16391696) but have never had any follow-up to it. For further context, the parent NSTextView for the NSTextTable-containing NSAttributedString is sitting within an NSScrollView/NSClipView combo, both in a view which is presented not by me, but by macOS' QuickLook engine. Cheers, Tony

I can change the file extension of my TypeScript files, you're right. But I can't expect my customers to do that too, especially when .ts is the de facto standard extension across all platforms. There needs to be a mechanism (even if it's only a "defaults write...") whereby the QuickLook system can be told 'treat any .ts files as com.microsoft.typescript and preview accordingly'. I could then offer that to my customers as a config option and warn them that this might affect .ts MPEG files they have. But so far, I can't even offer any kind of choice or solution. It's very frustrating!