Opus just calls CreateDirectory.
The Process Monitor logs you made earlier in the thread showed that the filesystem (or some other thing involved; OS, antivirus, etc.) is returning an access denied error from that request, even though it's apparently succeeding. That seems like a bug in the filesystem (or some other component between it and Opus).
It MUST be an issue with SSHFS. MKDIR fails too (same result). NEW FOLDER from File Explorer creates 4 new folders and doesn't refresh.
The only thing that works RIGHT is copying folders with File Explorer.
I got RCLONE working; error free and it is so much faster - I think I'll adopt this from now on.
Shazam - that's awesome.
Mine would refuse to copy ANY data. I literally thought this was a permissions problem on the share, and didn't initially assume it was a v13 problem.
Watch out for the vfs cache with Rclone, it tripped me up for a bit until I got it tuned and working correctly. May not impact you at all, but if you see odd things, check into that.
I added --vfs-cache-mode=writes to the mount and that seems to solve the issue. You're warning about using that? Or NOT using that? 
With this parameter, the file copy process for a large file is like 6x faster than SSHFS. Insane.
I did seen NSSM for running them as services. Very nice.
Thanks for pointing me in this direction. Not a LOT more work (just the initial config setup for the Steam Deck connection).
Definitely a bug in the filesystem. (Writing filesystems is hard!)
Worth reporting to the developers of it so they can fix it.
SSHFS hasn't been updated for like 4 years. LOL I shouldn't be surprised it has issues.
After seeing how fast rclone is? I might have to forgo SSHFS moving forward.