What is nfsd on macOS?
Solution 1:
nfsd is invoked by launchd while booting by the accompanying com.apple.nfsd.plist file in /System/Library/LaunchDaemons/.
As you can see close to the bottom of the following picture,
it's only kept alive, when /etc/exports exists. If the path doesn't exist, nfsd will not run.
So removing /etc/exports will disable nfsd temporarily until the path is recreated
or executing
launchctl unload -w /System/Library/LaunchDaemons/com.apple.nfsd.plist
will disable it permanently - even after reinstating /etc/exports (not recommended).