Hi, thanks for the quick reply!
So it's possible/likely that solved it. Before seeing your post, I found this: [solved] pi.hole resolves to 127.0.0.1 and added the two mentioned environment variables into my config, and removed the password variable, and this allowed me to login with the dns name.
I tried with the IP and it still would not let me login, but trying in a different browser (Chrome), I was able to get in via IP, and clearing history for the site on my main browser (Firefox) has allowed via IP to work as well.
Thanks so much for that suggestion! Feeling a tad silly I didn't think of such a basic step. Unsure how important those other variables are, but thought I'd mention they are not documented here: Docker - Pi-hole documentation