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. ...
I've the found following procedures, which I'm investigating now. Suggestions, comments welcome.
Clonezilla Live on Hard Drive
HOWTO - Starting clonezilla in batchmode from local hard drive with a custom-ocs (automated backup of hard drive)
I followed what wanadium suggested in comments (many thanks!) which solved the issue for normal users being unable to mount/unmount. Here is the line that had to be added to /etc/fstab
//remote-usrs-srv/Users$ /home/mylinux_username/drive_usr cifs users,noauto,rw,suid,exec,dev,iocharset=utf8,username=my_windows_username,domain=AD,vers=2.0 ...