brave://settings/content/autoplay
or (detailed path)
Settings | Privacy and security | Site and Shield settings | Additional permissions | Autoplay
Allow sites to autoplay videos [toggle switch to grey]
or
Block sites from autoplaying videos [toggle switch to red]
My experience: adjusting this switch lessens but doesn’t eliminate Autoplay.
The bar at the top of the Brave | Community page includes a ‘magnifying glass’ icon which searches within Brave | Community.
Click the ‘magnifying glass’ icon, enter ‘autoplay’, click, and …
… the fourth entry is:
which is very similar to your query. Amongst the replies, you’ll find mention of an extension that effectively blocks ALL autoplay - plus a discussion of risks associated with extensions.