Brave Browser is using 75% of the memory-that-is-being-used ← that is also not all the available memory … so Brave Browser is using approx. 70% of all available memory.
Brave Browser Task Manager window that displays column titles:
→ Task | Memory footprint | CPU | Process ID | Image cache | Script cache | GPU memory | JavaScript memory (<-- that creeps up)
When you add columns in the Brave Browser Task Manager window, they may not appear in that same arrayed order.
That monitoring, along with your Operating System’s monitoring that you have been using.