It should pop up when you have a nip07 extension installed like alby or nost2ext, or show you a button on the bottom left corner
Discussion
i'm using brave, and i have alby installed, and open. No dice. No button on the bottom left corner. I tried allowing popups and stuff, but still nothing.
Try using another browser. I just logged in from safari on my phone using the Nostore extension. So it should be a problem with brave for some reason