I also default to Vivaldi when I need to use a Chromium browser, and I have found that I like the Feeds part of the browser better than Thunderbird. It is for sure the most customizable Chromium based option, so many tweak-able options. Aside from a couple of RSS feeds I check like once or twice a day, Zen and FF are my defaults for basically all browsing. I don’t tend to do things that make use of the AI stuff in FF, but honestly don’t really care if Mozilla has those options as long as they keep them as easy to disable as they currently are.