> we know these don't give you the Vivaldi browser as they supply it.
how so? how do you know this?
You can test this locally yourself with mitmproxy, opensnitch, or whatever.
You can try building the (supposedly) open-source apps you use from source.
Everyone opining here should MitM themselves every now and then. If not for your own security then maybe to make sure you're not participating in psyop when opining online and resharing hearsay or old truisms.
Because they are open about including closed parts. Its not a FLOSS browser.