Shouldn't it be supported? Also is there a way to disable spotlight indexing on a mounted folder? mds_stores is going wild on fskit volumes.
mount -o nobrowse -t passthrough ~/Downloads ~/mnt
alexf@MacBook-Pro-3 build % mount
file:///Users/alexf/Downloads/ on /Users/alexf/mnt (passthrough, local, nodev, nosuid, noowners, noatime, fskit, mounted by alexf)```