Comment 2 for bug 1613403

Indeed fstype= is not currently supported by the kernel for umount. It is not difficult to add, but it has not been a priority.

The parser also needs a small patch, and it should of course be throwing a warning when fstype is not supported.

This at earliest could be supported in 5.11 if it is decided its important enough to spend a day on. Of course Ubuntu could easily pick the fix back to its released kernels if so needed.