For MacOS hardened Firefox esr which is the most stable version with extended security updates and harden it with the Arkenfox user.js customised to your own use case and threat level. It's commented extremely well and it will teach you a lot about browsers and what goes on behind the scene and networking. Otherwise there is Librewolf or better still the Mullvad browser both which are forks of Firefox, or even Floorp which isn't that bad but is based more on the BetterFox user.js which sacrifices some privacy and security in favour of better usability. There's also the Narsil user.js which is the most heavily secured and restrictive so will break a lot of sites. Arkenfox is a good middle ground of privacy and security versus usability, well commented, maintained and updated regularly.
https://github.com/arkenfox/user.js/
A user.js covers individual profiles and sits in your Firefox profile folder in you user home ~/Library/Application Support Think of this like your local preferences (about:config). I would also recommend you make use of a policies.json file which should be placed in a distribution folder inside the main application contents and covers all profiles /Applications/Firefox.app/Contents/Resources/distribution/policies.json and can be used for things like blocking automatic updates, telemetry, set up default search engines and a few other things. Think of this as your global preferences (about:config). Type about:about in the address bar and you will see a whole bunch of useful internal pages there.
https://support.mozilla.org/en-US/kb/customizing-firefox-using-policiesjson
https://github.com/mozilla/policy-templates
You can create multiple profiles in Firefox for different use cases and compartmentalisation. You can even run multiple profiles at the same time. I will also highly recommend the uBlock Origin add-on extension as a content blocker in either medium or advanced mode. uBlock Origin is designed and optimised for Firefox so you get full functionality. This extension is an absolute godsend.
For more info on hardening Firefox see the following site. Ignore all the political blog nonsense and memes on this site. The Firefox info is incredibly detailed and in-depth and all spot on. The guy knows what he's talking about.
https://12bytes.org/the-firefox-privacy-guide-for-dummies/
If you really get into the browser and know some CSS and even a bit of Javascript then you can go as far as styling the whole the browser to your liking using a userChrome.css and userChrome.uc.js file. Next level is then modifying all this internally at source level and building your own Firefox fork. No other browser comes close to Firefox but you do need to tame the Fox.
DO NOT USE FIREFOX AS IS BY DEFAULT
If you must run a Chromium based browser then I would recommend ungoogled chromium which has all the spyware removed and is signed with an Apple Developer ID and notarized.
https://github.com/ungoogled-software/ungoogled-chromium-macos/releases
Sadly at least one Chromium based browser should be installed due to some bad web developers designing around Google Chrome only so wont display correctly or will have issues with other browsers.
I'm not a fan of Safari. It's like swapping out Google spyware for Apple spyware, in fact Safari is worse as it's integrated deeply into the operating system which is never a good thing from a browser security perspective. You will also find that you will have problems with some extensions as Apple manipulates you into putting all your eggs in their basket. Be an Apple user and don't allow Apple to use you.