Vivaldi also kept Manifest V2, so old extensions do keep working there. They also have a mastodon server, and email/calendar/feeds, so they offer more out of the box than Firefox. Lots of projects built on other open source projects like Chromium and KDE do offer legitimate alternatives.

OSM from F-Droid is the way, but there are a lot of apps now based on OSM data that are also very good like organic maps. It can be hard to switch over metadata, and you might lose some of the conveniences, but it’s manageable or even better for some uses like hiking.

I switched to Vivaldi and Ecosia, barely notice a difference.