I have my user in the wheel group and in sudo’s config I have %wheel… nopasswd(not exactly like that in config, just general idea). When I use sudo, it still prompts for my password anyway.
I have verified that yes my user account is in wheel. Opendoas works as expected, but not sudo
Did you reboot to get new group value after editing group file? (I ask because I did that once)
check as root /etc/sudoers.d, if there is a file present delete or modify it, because the file overrule the configuration in /etc/sudoers
You can check your current config with sudo -l. Might help