Yes, Vivaldi is based on Chromium.
Also, (it's UI isn't open source.)[https://vivaldi.com/blog/technology/why-isnt-vivaldi-browser-open-source/]. Not much of an issue, given all popular browsers aren't either (except Firefox).
There is a vocal contingent of people online who hate that chromium has the vast majority of market share of browser rendering engines.
Your response makes it seem like you don't agree with the efforts of those vocal people. Which is funny, because you're posting this on lemmy, instead of reddit, so you clearly don't like a single company having complete and monopoly-like control, the browser wars should be viewed the same way. Non-Chromium browsers (but mostly Firefox) are the only thing stopping Google from having basically complete control over the internet, by having only 1 dominant rendering engine that they control.
Here's a perfect example: https://www.tomshardware.com/news/youtube-responds-to-delayed-loading-in-rival-browser-complaints
Good news! Firefox is my primary browser, but I use vivaldi as a secondary browser and since it is on all the devices, I sync it for notes.
I use my steam deck as my portable computer instead of a laptop these days, and finally I can add vivaldi to it.
Awesome!
I use
Mull Browser
from Mullvad as my primary browser, but before Mull Browser I've been using FF.