The BCM4321 wireless adapter rarely works, sometimes it does after reboot if there's a bit of luck. Never on the live disk, where the driver in the Manjaro Settings Manager is marked as uninstalled.
It could happen that it lists the available networks but that it doesn't allow connecting, or that it doesn't list any network at all. I have tried finding a pattern but I have been unable.
- Installing the driver using the Manjaro Settings Manager.
- Installing the DKMS version of the driver.
- Similar solutions in this forum.
- Disabling the power manager "TLP".
- The solutions in the Arch wiki.
- Removing all wifi modules, then probing them one by one.
Probing the module b43 actually activated and deactivated the adaptor, but it wasn't unable to connect to the listed networks in a consistent way. Even by forcing b43 to support all hardware.