If you run that on that client that couldnt resolve pi.hole via nslookup, I guess this is somehow Docker settings related.
Am not that proficient yet with Docker.
Cant help you with that ... sorry.
EDIT: Ow ps, I should have queried my other Pi that is up to date
Usually the default docker network uses 172.17.0.0/16 subnet range.
Using macvlan network, the subnet range should be the same as range used by the host.
I never saw a docker subnet using this range. I'm not saying this is wrong, but it looks unusual/unexpected.
I shouldn't be, but that isn't to say I'm not. I have been wrong plenty of times before. The OS is ubuntu server 22.04 so I shouldn't have desktop version. I think I'm going to try wiping docker and reinstalling. I only changed one item in Pi-hole so I won't loose anything by wiping it.
Note: The only setting I changed in Pi-hole was adding a domain name for my router since Asus requires it for some reason. (After rereading my reply I expected future me to get asked that)