I just set up from scratch on FreeBSD and had that issue at first as well. Turns out the instructions on the website could use some love as the ansible nginx configs were out of date. I manually updated my nginx config to match the blocks for UI and BE in the nginx_internal.conf and that seemed to resolve my registration issues.
Also make sure you’re front end version is the same as your backend. I also made that mistake.
Where did you find that new lemmy.conf file? I have no idea what options are even available in that config. I saw a limited one in lemmy-ansible but I know for sure there is more than what’s in there as an option.