We haven't done this because that would require more work on checking the UNC path.
For instance, \\..., \\UNC\....

Ideally, after prepending, it would look like: \\?\\\UNC\...

See more information in https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#maximum-path-length-limitation

"The "\\?\" prefix can also be used with paths constructed according to the universal naming convention (UNC). To specify such a path using UNC, use the "\\?\UNC\" prefix. For example, "\\?\UNC\server\share", where "server" is the name of the computer and "share" is the name of the shared folder."

(In reply to Tom Tung [:tt, :ttung] from comment #0)

"The "\?" prefix

Did markdown unescape \? it should be \\?\.

(In reply to Masatoshi Kimura [:emk] from comment #1)

(In reply to Tom Tung [:tt, :ttung] from comment #0)

"The "\?" prefix

Did markdown unescape \? it should be \\?\.

Right, \\ was transferred to \. I updated the comment. Thanks!

This will need to consider IsBlockedUNCPath (Note: there is two checks in the same file)

Dropping myself from the assignee since I won't work on this in the short term.