just off the startup of brave from the task manager as much as i know brave will start only when you open it and all the tabs too.
there is another way of doing this where you can put the tabs you use the most and frequently ‘pinned’ by right clicking on it and selecting pin tab which also minimizes it into a box which kinda looks minimal too. then go to setting and choose save memory by making inactive sleep this might help the app to focus on the pinned tab rather than the other ones and during the use the other tabs might be in sleep. note that sleep tabs might sometimes need refresh. also as a tip close the browser with the hometab selected.
let me know if this helped