I would like some suggestions on the best browser for my iMac 10.15.7 Catalina?

I use Firefox on Catalina 10.15.7. Works great and I have never had any problems with it. Plus, Mozilla keeps it up to date with security & functional updates and there are quite a few security & other types of plugins that add functionality. The security plugins I use are Privacy Badger, HTTPS Everywhere and uBlock Origin. (Although I may no longer need HTTPS Everywhere because Firefox now has its own built-in HTTPS-only mode.)

On very rare occasion I switch to Safari when some website doesn't work correctly with Firefox. But this is rare. Apple does update Safari but most of the time the update is associated with a new release of macOS. Catalina is now "4 generations old" and does not get any more updates.

charm61 wrote:

I was using duckduckgo through Safari but it's now saying my browser won't support it.

I don't understand exactly what is saying Safari doesn't support DuckDuckGo. Can you elaborate?

To answer your question Brave is excellent, and it incorporates its own Search Engine. I am not familiar with Vivaldi.

I prefer Brave or Opera, but...

Thanks to A Brody, Browsers by Mac operating system…

Browsers by Mac operating system - Apple Community

I recommend Firefox as a good 2nd choice for a Catalina Mac.

When I bump into some problematic website on Safari, I can usually get things done if I launch Firefox. 👍🏽

Firefox

Firefox

I like Brave because it lean and it automatically comes up in Dark Mode which I need. Firefox is a very good browser but I find it more difficult to customize it.

charm61 wrote:

I was using duckduckgo through Safari but it's now saying my browser won't support it.

I second John's question…

John Galt wrote:

I don't understand exactly what is saying Safari doesn't support DuckDuckGo. Can you elaborate?

the DuckDuckGo search engine works fine in Safari running on Catalina 10.15.7.