Debian ships only free firmware by default, so most wireless chipsets need an extra package before the adapter works at all.
Enable Wireless Firmware
firmware-misc-nonfree bundles the non-free firmware blobs for common wireless (and other) chipsets that Debian’s default install excludes for licensing reasons.
AWUS1900 (Realtek RTL8814AU)
The Alfa AWUS1900 USB adapter uses a Realtek RTL8814AU chipset, which isn’t supported by Debian’s in-kernel driver. realtek-rtl88xxau-dkms builds and installs the out-of-tree driver via DKMS, so it survives kernel upgrades.
Cheatsheet
Enable Wireless Firmware
sudo apt install firmware-misc-nonfreeAWUS1900
sudo apt-get install realtek-rtl88xxau-dkms