Why stop at browsers? When you take your phone out of the box it should ask you what OS you want: Android, Plasma, PureOs, Tizen, BSD, Ubuntu, fedora, Arch, SuSE. Then you have to pick your window manager: DWM, Flux, Qtile…. Then you pick your filesystem: Reiser, NTFS, Ext4, ZFS. And so on. After all you need to be fair right?
Apple should’ve taken the easy route and offered an optional bare metal phone with hardware only in the EU. Totally not locked down and no security or encryption. You install everything yourself. That would’ve met all the mandates.