My sequence of replies, above:
“Brave isn‘t downloading Videos to the playlists anymore properly - #22 by 289wk”
and the next . . .
I consider, that Brave Browser iOS is holding on to downloaded “tasks” - that somehow linger: scripts that should not remain, and some scripts are piling up (including, their running in the background).
In your case, where you have a lot of data traffic:
“Excessive Cellular Data Use - #5 by theLost”
I would consider that the bug I found and mentioned above, might be a contributing factor.
You might use the iOS App Privacy Report, in order to see what un-expected traffic is occuring.
The Brave Community webpage for your issue, is closed - thus, my writing, here.