So, this appears to be working 100%. The system says it is Ubuntu 20.04.4 LTS. I has the Mate GUI on top which may or may not affect things. @Bucking_Horn pointer to this reply tells how to get systemd-resolved out of the loop. I think one key thing is to remove the symlink so NetworkManager writes a valid /etc/resolv.conf
I set my router to give my pi-hole the same IPv4 address (question about this later).
I then installed pi-hole using the recommended curl ... | bash command and it all went well.
I then used this page to install and set up unbound.
It all went like clockwork once systems-resolved was out of the picture.
The DHCP server is on the router. The DNS it gives out is for the router but it is forwarding it to the pi-hole. Originally, it would not accept that address but I think I know why. In any case, I got it to accept the address finally.
My last question: The router has an entry for a DNS for IPv6 and so I put the global unique IPv6 address in for the pi-hole. I tried putting in the IPv6 address that comes from the MAC address but it wouldn't take it. My question is, is this address stable? There isn't a facility like there is with the IPv4 DHCP to pre-allocate hostnames and IP addresses based on MAC addresses with this router. And it appears the IPv6 prefix is given to the router as well. What are the recommendations for this?