For anyone maintaining a hetrogeneous network utilizing Linux NFS servers, when I upgraded from 20.04 to 22.04 on our mail server which exports the mail spool to various machines, most using version 4.2 over TCP NFS but some using version 3 UDP and one using version 2 UDP, it broke all of our machines mounting using version 2 or version 3 NFS even though rpcinfo -p showed these protocols exported.
It turns out that what changed is capabilities and defaults. All three NFS versions are supported, but all now DEFAULT to TCP only. This makes ZERO sense as UDP was the only protocol available in the NFS version 2 and version 3 specification.
However, it is configurable and now everything is back in service and I can move forward with updating the rest of our machines that are 20.04 to 22.04, however I am going to hold off on that until I get my car back from the shop as that such upgrades often result in disasters leaving a machine unbootable and requiring in person attention.