(EDIT March 24, 2021, we have a NEW UPDATE about Big Sur. Click Here to read this information that is newer than what is posted below).
If you already own an ALFA 802.11ac USB WiFi booster and have followed our steps to get it to work on Mac OS 10.15 Catalina, you may be wondering if you upgrade to Big Sur (released by Apple today, November 12th), if your product will still work after the update. Operating system upgrades can often times break hardware.
The good news is we have tested it today and can confirm with the 11.0.1 release the ALFA AWUS036AC and AWUS036ACH still work well.
We have not yet confirmed if you can do a new install the same way you can on Catalina. So if you do not yet own an ALFA AWUS036ACH and are looking to get one and install it on Big Sur, we have not yet confirmed the installer will work. We should have an update on that in the next few days and will post to our blog.
Military and First Responder 
the same issue, it doesn’t work on big sur,
please provide a new update
I have an ALFA AWUS036ACH but the recommended driver fails while installing and does not work on macOS Big Sur.
just updated from catalina, realtek tool does not find the adapter (alfa awus036ACH). tried to renstall the pkg of catalina: failed the installation. please help me i’m without wifi connection :(
The AWUS1900 & AWUS0336AC* series are not currently compatible with Big Sur new installations. We do not have an ETA on if/when a new installer will be released for Big Sur.
Same issue here. Alfa AWUS1900 not working with Macbook Pro ( macOS Big Sur 11.0.1)