There might be a package called kio5-extra, maybe something is still relying on that?
Are you talking about cifs?
AFAIK NFS does not work with credentials that way, you can set up access limitations on the server (or rather, you have to open up the server), but not with usr and passwd in that way.
NFS is like you connecting a physical device, but it is over the network. (completely different from for example smb, ftp, sftp etc)
You will use the user you are on the guest, not a username. So the UID on the server has to be the same as on the host. THAT is how credentials are handled on NFS.
Teaching time
Caveats of this compared to samba is that you can use it as a normal filesystem, changing credentials with for example chown and chmod (or right click in Dolphin), witch you CAN NOT on samba. (just remember that it is the UID, not the NAME of the user that matters, so make sure users and groups have the same UID and GID on both machines)
Moving files from one NFS directory to another is made directly on the server. On SMB it would be transferred VIA the host, so if you only have lets say 100mbit network (if you use a vpn tunnel over the internet for example), that is the speed limit on a move.
With NFS the speed limitation is the servers hard-drives and bus interface (just like if you were sitting on the server and moving the files, so probably GiB/s if you have ssd:s)
Same with copy ofc.
If you want me to spit out a small tutorial for using systemd.mount, I can, but it really sounds to me you want to use Dolphin here, and then that solution might not be the best.
I think the question you should ask here is:
How do I use nfs:// in Dolphin to connect to my nfs server?
(what does typing nfs:// in Dolphin actually do?)
If you get that answered, I think you can find a solution of how to automate it.