I'm using Vivaldi, which is basically chrome, with much better user experience.
It supports the same features, as it uses the same rendering engine, same JS engine, same everything.

Despite that I get a message that my browser is unsupported.
My guess is that instead of feature detection you do a browser detection and if it does not fall into the bucket of Mozilla or Chrome, you stubbornly show a message about the browser being unsupported without even giving the user an option to take the risk and go through with their browser.