[deleted] I'm seeing the same thing with Brave, version 1.69.153, also with shields off. Weirdly, when I try the same using Brave on stock PixelOS, I don't have the issue. With the same version of Brave, shields on.
When you select "Sign in" there is a popup ("Download the free app designed for your phone!!!!") that should appear before you can continue to the actual sign-in page. I would've assumed that the issue was caused by Brave and Vanadium blocking that popup as part of their ad blocking, but it doesn't seem to be the case. One of life's mysteries.