This comment only serves to help OP an not debug the reason NFS boot doesn't work.
I was able to boot the iso using http only:
kernel ${boot-url}nfs/focal/casper/vmlinuz initrd ${boot-url}nfs/focal/casper/initrd imgargs vmlinuz initrd=initrd boot=casper ip=dhcp url=${boot-url}ubuntu/focal/ubuntu-20.04.1-desktop-amd64.iso maybe-ubiquity boot
If you find out how to boot via NFS I'd like to know how. :)
This comment only serves to help OP an not debug the reason NFS boot doesn't work.
I was able to boot the iso using http only:
kernel ${boot- url}nfs/ focal/casper/ vmlinuz url}nfs/ focal/casper/ initrd url}ubuntu/ focal/ubuntu- 20.04.1- desktop- amd64.iso maybe-ubiquity
initrd ${boot-
imgargs vmlinuz initrd=initrd boot=casper ip=dhcp url=${boot-
boot
If you find out how to boot via NFS I'd like to know how. :)