Well, users wan't to sync...
Firefox under iOS sucks, and under Android it's okay, on Windows and macOS it's fine.
Brave Browser and privacy lol that was a joke, wasn't it?
E.g.
https://wccftech.com/privacy-centered-browser-brave-is-in-hot-waters-for-violating-users-confidence/
Safari, no Windows version, no way to cross platform sync.
Microsoft does not sell data, the ones who says Google, Microsoft or Apple sells user data just proves that he/she absolutely has no technical knowledge. They use your data to sell ad slots, but your data isn't safer with Apple than with Google, nor with Google than with Microsoft and vise versa.
The ones who violated privacy is exactly Brave Browser...
OpenSource is no warranty for privacy, the distributed binary can(and probably does) differ to the open sourced code.