How to configure BT+AC600 Wi-Fi dongle on Arch Linux

I purchased a Dell OptiPlex 3050 CPU to install Omarchy Arch Linux as my backup development machine. Most of my experience is with Debian/Ubuntu, making this my first attempt at using Arch Linux. This is a summary of the steps I took to get it up and running.

First, visit https://omarchy.org/ to download the ISO. Since I'm using a Mac, I needed to use Etcher https://etcher.balena.io/ to create a bootable USB. After installing Etcher, the process is straightforward: select the ISO image and the USB drive you want to use.

Once you have the bootable USB ready, connect it to the CPU and power it on. During startup, press F12 to open the quick boot menu, but initially, I didn’t see the USB option. After some investigation, I discovered that I needed to disable the Secure Boot feature in the BIOS menu. Once that was done, the USB option appeared, and I was able to boot from it.

Follow the installation steps for Omarchy, answering the prompts as needed. The file copying process takes some time since this machine is running an Intel i5 CPU. After the installation finishes, an error will appear because it is trying to connect to the Internet, but my Wi-Fi dongle wasn’t recognized during the installation process. I had to restart the computer to proceed manually.

After rebooting, I could log in and open the terminal, but I still had no Internet connection because the Wi-Fi dongle was not configured. After a lot of troubleshooting with ChatGPT, I realized I didn't have the lsusb command available. So, I ran

lsmod | grep 88

to check for kernel modules, but I found that none were installed, requiring a manual offline installation.

Running

sudo dmesg | tail -n 30

helped me gather information about the dongle. I connected and disconnected it to see messages like this:

usb 1-1: new high-speed USB device number 4 using xhci_hcd
usb 1-1: New USB device found, idVendor=0bda, idProduct=c811, bcdDevice= 2.00

In my case, I found:

idProduct=1a2b and idVendor=0bda

I tried to enable the kernel module with:

sudo modprobe rtw88_8821cu

But it didn't work.

After more troubleshooting, I discovered that the USB dongle operates in CD-ROM mode. Many Realtek devices do this to enable Windows to auto-install drivers. Therefore, I had to install usb_modeswitch.

I returned to my Mac, formatted the USB stick that initially contained the ISO, and manually downloaded usb_modeswitch from Arch Linux's package repository (https://archlinux.org/packages/extra/x86_64/usb_modeswitch/download/). The only additional requirement was Tcl (https://archlinux.org/packages/extra/x86_64/tcl/download/).

I copied both files to the USB stick, plugged it into the OptiPlex, mounted the USB to the filesystem, and installed the packages with the following commands:

sudo pacman -U /path/to/usb/tcl-8.6.16-1-x86_64.pkg.tar.zst
sudo pacman -U /path/to/usb/usb_modeswitch-2.6.2-1-x86_64.pkg.tar.zst

After installation, I ran:

sudo usb_modeswitch -v 0bda -p 1a2b -K
sudo modprobe -r rtw88_8821cu
sudo modprobe rtw88_8821cu

Finally, I connected and disconnected the Wi-Fi dongle, and it worked!