When strict isolation mode is enabled, embedded video or media playback is broken. Users are unable to interact with embedded video or media (they will see a player, but will be unable to click on the play button, etc.).
I have tested this with two embedded players: a SoundCloud embed and a Vimeo embed.
The SoundCloud embed is here (the O’Reilly Podcast with Brendan): https://www.oreilly.com/ideas/the-web-is-broken-lets-fix-it
The Vimeo embed is here (the recent tab improvement blog post): https://brave.com/new-brave-version-features-tab-improvements-for-enhanced-performance/
Reproduced both times reliably. When strict isolation mode is enabled, one cannot interact with the embedded players. When it is disabled, they work as intended.
I’ve seen this +1’ed on the BATProject subreddit, and potentially related issues here in Brave Community (e.g. with embedded players on Twitter).