The first paragraph of the article states the code is "Microsoft-approved, largely Samsung-authored". The code is open source and missing features, if any, could be added. Microsoft has explicitly endorsed its usage in the kernel [0] and its architecture is fully documented [1]. What more do you want?

[0] https://cloudblogs.microsoft.com/opensource/2019/08/28/exfat...

[1] https://docs.microsoft.com/en-us/windows/win32/fileio/exfat-...