I use RHEL 7.9, and for what it's worth I am disappointed with NFS 22 years into the 21st century....
my experience is if you edit /etc/nfs.conf or /etc/sysconfig/nfs then the mount often defers for version 3. For me, again in RHEL 7.9 I can't speak for other distributions, to get NFS v4.1 working I must not change anything in either of these two files, and then at best only v4.1 will work; I have never been able to get NFS v4.2 to work even though it is listed in /etc/nfs.conf.
So, make sure between your nfs server and client, all the details within /etc/nfs.conf and /etc/sysconfig/nfs match, the things like mountd and statd port numbers... by default it should all inherently happen under port 2049 for NFS4. If there are port number discrepancies between the nfs server and client, that will prevent the mount from happening.
for reference, here is the bare minimum needed:
on nfs server in /etc/exports have /bkup *(rw,no_root_squash) then do exportfs -av followed by exportfs -s to validate.
on nfs client a simple mount 192.168.1.1:/bkup /bkup should mount {change ip address to match your nfs server, and folder name accordingly}.
also do a service firewalld stop along with a setenforce 0 to turn off the firewall and turn off selinux, respectively. I don't think selinux typically prevents nfs, but one step at a time to get mount working... what I've mentioned here has always gotten nfs to at least work. hope that helps.