[JasonB]

Yes, the inconsistency is absolutely bizarre.

As you no doubt know, what you get with Safari is how it's supposed to be. What you're seeing with Brave is actually the mobile phone arrangement of the screen, which shouldn't show at that sort of screen size.

I wonder if there is somehow a persistent cache of a temporary glitch? It's probably unlikely but since it's really simple it might be worth following these instructions to bypass your cache