Do you know what it is that makes it appear on some websites but not others?
Now I know it’s a web app I found the appropriate Brave help page and I see I always have the option to do it via ‘Save & Share’ menu option but I’m still curious why it’s only sometimes in the address bar.
The site needs to be built as a progressive web app, which adds a couple of extra requirements to the website. It essentially allows it to behave in an app-like way when “installed”.