A network adapter not being detected properly (or a hard block) can sometimes be hard to correct. Changing the BIOS settings may help in this situation (as well as power cycling). If available, a BIOS update may also help correct these problems. Below are several methods that may help with raising your adapter.
Resetting the BIOS back to the factory default settings may help with adapter detection. This also sometimes helps to remove a hard block. Boot into the BIOS settings utility and reset the BIOS back to the factory default. Save the default settings, and power down the laptop.
Disconnect any other network devices that do not require troubleshooting. This includes LAN cables, USB to Ethernet adapters, and USB phone tethering.
Power down the laptop and remove the battery and power plug. Let the laptop sit without power for a few minutes. Then, hold down the power button for approximately 30 seconds. Pressing the power button will help drain all left over power from the unit’s motherboard.
Then reattach the AC power (no battery), and restart. Boot into your bios, then reset the bios to the factory defaults, save the default settings. See if it will boot correctly with the factory default settings. If not, you may have to change a few settings in the BIOS (such as secure boot) to get Manjaro to boot correctly. After rebooting your adapter may be properly detected and initialized.
Be sure the following boot parameter is in place (do not remove it).
The following command will add a GRUB kernel boot parameter to /etc/default/grub:
sudo sed '/^GRUB_CMDLINE_LINUX_DEFAULT=/s/"$/ pcie_aspm=off "/g' -i /etc/default/grub
After adding the boot parameter(s) and saving your changes, run:
Reboot, and test your connection for improvement.
*sed magic courtesy of @dalto