To use your own domain name for the forum, follow these steps:

In "Administration - Domain Name" add the domain name that you have registered.

For example: example.com

In the management of DNS zones of your domain registrar, add "CNAME record" eg:

example.com. IN CNAME forum.mybb.ru.

_acme-challenge.example.com. IN CNAME _acme-challenge.forumcdn.ru.

The last record is required to issue an SSL certificate for your domain.

Some domain registrars do not support specifying a CNAME record for the primary domain. In such cases, add an A record instead:

example.com. IN A 91.194.2.84

_acme-challenge.example.com. IN CNAME _acme-challenge.forumcdn.ru.

Wait for DNS update. This process can take up to several days.

If you did everything correctly, the status of the domain will automatically change to "Working".