I've stopped searching about this topic and I will continue in the future but these are what I'd found.
They've added this man page to newer Ubuntu distros: http://manpages.ubuntu.com/manpages/focal/man4/pnfs.4freebsd.html
And in ubuntuforums an active member said:
From what I have read, kernel 4.12+ has supported pNFS which means
Ubuntu 18.04 and higher. NFS protocol 4.1 was the version that had
built-in support for pNFS.
I have not done this before but from what I am seeing, there is not a
flexible way of setting this up regarding redundancy and scalability.
How to configure the data servers for a pnfs metadata server?
I also have not to see ANYTHING "comprehensive" regarding this
subject. There are some bits and pieces about setting it up but
nowhere have I found someone steps thru the entire process and then
proceeds to show any test results showing how it is any better than a
standard NFS design...which has many comprehensive setup guides.
I will do some practice and share them here if I get positive results in the future.