How to add a custom search engine?

Brave Browser Desktop Support
,
2

I suggest that you study the replies by Brave Support team member @Mattches - regarding how to add search engines:

All search engines are suddenly gone, except the default one - #18 by Mattches

All search engines are suddenly gone, except the default one - #23 by Mattches

All search engines are suddenly gone, except the default one - #25 by Mattches