When I used Brave today I got a HUGE message on my computer screen that said my computer has been hacked with Brave and I should call the number on the screen. The screen was locked and I could not exit. I tried Brave a few hours later and it was the same. I just uninstalled Brave and reinstalled it and it was ok, I used another browser and the computer was fine, so I know there was nothing wrong with the computer.
The type of screen you’re describing sounds very much like a bad actor attempting to scam you out of some money. Typically with attacks like these, users will appear to be “locked out” of their browser and encouraged to call some phone number in order to get the issue resolved. Calling this number results in the scammer pretending to be tech support of some kind and charging you money to fix a non-existent issue.
It’s unlikely that you ever actually had a virus of any kind, especially if un/reinstalling the browser resolved the issue. To be safe, run a virus scan on your system and make sure nothing is detected.
Do you happen to know what site(s) you were browsing when this “alert” first appeared?