I just tried to reproduce the issue on Debian 11, and guess what, the issue DID manifest its self on Debian as well.
kajetan@debian:~$ sudo mount -v -t nfs -o vers=4.1 optinas1:/volume1/test_nfs_share /var/test_nfs_share/
mount.nfs: timeout set for Tue Aug 30 16:33:58 2022
mount.nfs: trying text-based options 'vers=4.1,addr=172.22.1.49,clientaddr=172.22.1.100'
mount.nfs: mount(2): Permission denied
mount.nfs: access denied by server while mounting optinas1:/volume1/test_nfs_share
Moments later I executed the same command on pop!_os
code_text:
kajetan@pop-os:~$ sudo mount -v -t nfs -o vers=4.1 optinas1:/volume1/test_nfs_share /var/test_nfs_share/
mount.nfs: timeout set for Tue Aug 30 16:33:32 2022
mount.nfs: trying text-based options 'vers=4.1,addr=172.22.1.49,clientaddr=172.22.1.51'
kajetan@pop-os:~$
And the mount worked fine. It looks to me like somewhere along the chain (Debian -> Ubuntu -> Pop!_os) the issue got fixed. And yes, I did apply
apt-get update && apt-get upgrade
to the Debian box.