Those Apple computers with their Broadcom chips are always causing problems. Do me a favour and please run this command and post the output:
hwinfo --netcard --bluetooth | grep -Ei "(speed|hotplug|model|status|cmd|file|detected|driver:)" | grep -v "Config S"
Why don't you try running this command then test your wifi:
sudo systemctl stop NetworkManager; sudo modprobe -r wl; sudo modprobe -r brcmfmac; sleep 3; sudo modprobe brcmfmac; sudo systemctl start NetworkManager
There should be at least one error generated by the last command, please post the output generated by the last command as well.
Welcome to the forum BTW.