To my knowledge this isn’t typically done. I mean, usually individual sites have a thing that says “Remember Me” or something where it will automatically fill in your username when you visit their site.
The only other thing I can suggest is that you tell it to remember your Login, but then you can go to your Passwords at brave://settings/passwords and Edit it. It won’t let you leave it blank but you could put a single digit, such as 1 and then hit Save. Next time you go to that site, it will show username and put in the single password, but you’d just delete the one character and put in the real password.
There may be other things out there, but to my knowledge, that’s your limited options within Brave itself without getting any extensions.