I know in GrapheneOS that the Google Play Services are sandboxed and you can install them in a specific user profile, but I’m not sure if doing that still gives you notifications across those profiles

Hopefully someone with a little more knowledge of this can help? lol

By default, sure. But uBlock is way more powerful when you configure it. Seriously, take a look at their wiki. I doubt that Brave lets you choose exactly which domains to connect to on a per-site basis. And do you really want an advertising company to make your adblocker? They’ve done shadier stuff.