There is a bug when Brave is on full screen, you watching a video into full screen and when you escape from full format it change brave into windowed… It’s very disturbing !
Could you give us some more details such as brave info (brave://version), are you using desktop or mobile, reproduction step?
I’m using : Brave
1.5.115 Chromium: 80.0.3987.149 (Official Build) (64bit)
On Windows 10 OS Version 1909 (Build 18363.720)
When i use the full screen on youtube for example, then i click on real/virtual escape button, brave become windowed instead of taking all the screen