more NFS woes

I am happy now with using NFS to share files between RISC OS and Mac Os. There are a few mysteries but no serious problems.

Repeating the process for RISC OS and Linux has not gone as expected.
Omni does not seem to be able to see the Linux server. Although I have no problem with the same shares on a Mac.

Here is the setup:

Raspberry Pi with  Raspbian Bookworm
------------------------------------
/etc/exports
    /home/riscman/shared *(rw,all_squash,insecure,async,no_subtree_check)

Mac Mini Mac OS
---------------
The shared directory can be seen in Finder:
    Network > 192.168.1.27 > shared
    files can be edited deleted etc

On ARMX6 RISC OS 5.29
---------------------
    Choices: Omni.Mounts
        NFS,pishare,O,192.168.1.27,/home/riscman/shared,nobody,,

   Clicking on Omni >Mounts >pishare
    gives:
        RPC communication failed on mount
        (RPC service not available on remote host(not registered))