What is nfsd on macOS?
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).