In window-mode (as opposite to full-screen), Brave displays the colored buttons for close, minimize and maximize in the top left window corner, aligned with the tabs. This is perfect. But when the window is maximized to full-screen, the buttons disappear. Instead, when moving the mouse to the top of the screen, an additional title-bar appears above the tabs. This is unnecessary. The three buttons should stay aligned with the tabs bar, even in full-screen mode and this additional title bar should not appear at all.
Still in full screen mode, there are a few pixels above the tab (between the tabs and the upper screen border) which are actually only wasted screen space. the tabs should align with the upper screen border.
Still in full screen mode, when the mouse pointer is moved to the top of the screen, the whole Brave window slides down to make space for the macOS menu bar. Instead, only the browser interface, but not the web page content, should move down.
In order to demonstrate how my three suggestions should work you can try Yandex Browser. It’s also a Chromium based browser but unfortunately not open source, therefore the code for a possible implementation of these changes cannot be take from there.