I have this same problem.
cmd+shift+F toggles the toolbar in fullscreen, but it does not make the toolbar appear only on hover, as OP queried.
Big Sur 11.4 Brave Version 1.25.73 Chromium: 91.0.4472.106 (Official Build) (x86_64)
I have this same problem.
cmd+shift+F toggles the toolbar in fullscreen, but it does not make the toolbar appear only on hover, as OP queried.
Big Sur 11.4 Brave Version 1.25.73 Chromium: 91.0.4472.106 (Official Build) (x86_64)