How to install driver for broadcom 43142

# echo "blacklist bcma" > /etc/modprobe.d/broadcom.conf
bash: /etc/modprobe.d/broadcom.conf: No such file or directory

# echo "wl" > /etc/modules-load.d/wl.conf
bash: /etc/modules-load.d/wl.conf: No such file or directory

You need to create the directory with mkdir -p /etc/modprobe.d /etc/modules-load.d before running these commands.

# modprobe wl
modprobe: ERROR: could not insert 'wl': Required key not available

For out-of-tree modules you will need to disable module signature enforcement as described here:
https://docs.01.org/clearlinux/latest/guides/kernel/kernel-modules.html#load-kernel-module

That should get the module to load but you’ll also need the right firmware as described in the links you posted.