You can use any browser you want, just be aware of what the downsides are when you do.

The issue with Chrome and Chromium based broswers is the power that Google exerts over the internet via the Blink engine. Although other companies use the same technology, Google controls it and shapes it for it's own commerical gains.

The other big alternative is also proprietary with Apple's Sarfari and WebKit ecosystem.

Vivaldi is a nice browser but it is still run by a private company and it still monetises you to an extent. In vivaldi's case it is currently fairly inocuous - they have referral deals with search engines for the default search, and deals with companies for default bookmarks. But it seems to be currently a more trustworthy browser. Ultimately though, it is part of the Blink ecosystem and supports Google's increasing domination of the browser engine space.

Mozilla and Firefox remains the only truly independent browser, run in a not-for-profit and fully open source way, on the Gecko engine. It's existance helps maintain the neutral aspects of the Web - instead of sites being designed for one browser, it encourages web site and services to be truly standards compliant. Firefox monetise users in a similar way to Vivaldi but that money is used to actually maintain and develop Gecko and other Mozilla technologies, while Vivaldi use that money to maintain Vivaldi the company - they don't need to fund most of Blink as it's made available by Google.

But no one is obliged to support Firefox or open technologies. It's a personal choice what browser you use and there are many valid reasons beyond open standards to chose a browser. I use Firefox for multiple reasons; I genuinely like it and am used to it, but I actually also use Vivaldi and even Chrome on occasions (sometimes to view crapily designed ad heavy or tracking sites without having to disable lots of privacy extensions etc in firefox to make it work; I use Chrome as a bog standard sandbox when I want to dump crap sites out of my main browser but still want to quickly view it for whatever reason).

Pick a browser you like and don't feel guilty if that happens to be chrome based.