[*.]example.com will work for the current page but subsequent pages that contain a modification to the parent URL, such as google.com becoming accounts.google.com, require their own allowed settings. This slows down browsing on first visits to sites when setting up permissions.
https://[*.]example.com will work for all URLs with varying prefixes thus allowing a more straightforward browsing experience (if you trust the parent website).
I think https://[*.] is Brave’s intended behaviour rather than [*.] that is provided as an example.
I hope this helps.