They are offering a service to check whether they have leaked your passwords or not, you just have to give them your passwords for them to check.
I don't see any reason to give anybody my passwords, no matter what they claim.
Imho the healthiest way over the internet is: trust no one.
However, it's a good way to check how good is their password manager implemented


Do you mind me asking are you using chome? I'm wondering why google doesn't even recognize I'm using an chromium-based keyring to encrypt passwords

Probably something Brave did so Google can't recognize jack shit. It's good to see their password manager works to keep themselves out though, that's useful!