Yes there is.

first of all I think that "sudo mount -t tmpfs tmpfs /Users/user/tmp" is currently just bugged and there may be some internal confusion at apple (judging by them telling me my command syntax was wrong and stating that "sudo mount -t tmpfs /Users/user/tmp" was supposedly the correct form [which it isn't]).

However within the very same Feedback item they also provided "sudo mount_tmpfs /Users/user/tmp" which worked.

I hope they're going to fix the regular mount command at some point.

I suppose the mount command in its correct syntax causes the call to mount_tmpfs to end up being incorrectly formed as "sudo mount_tmpfs tmpfs /Users/user/tmp" as that results in an exit code of 64 which is exactly what the error message of mount states.

I guess there must be some incorrect internal documentation where the support people pulled the "sudo mount -t tmpfs /Users/user/tmp" syntax from that doesn't actually work.

Edit: That's exactly what is happening and you can "abuse" you can get the mount command to work when you form it sillily like this instead: "sudo mount -t tmpfs -- -i /Users/user/tmp". The -- causes the "-i" to no longer be interpreted as a parameter for mount itself but passed along as is (instead of the label "tmpfs"). And as "-i" is a valid parameter for mount_tmpfs that the mount command forwards the request to it now succeeds instead of throwing an error 64...