From: https://www.thinkpenguin.com/gnu-linux/networking-devices
This works on Debian Buster. Previously updated firmware-realtek to the backports version. I don’t think it maters, as the symptoms were as below before and after.
If you are on Ubuntu 17.04 or Debian 9 and possibly other distributions and you see a list of access points, but can’t connect try this (it works around a bug that prevents users from connecting to a network with a USB wifi adapter):
Edit /etc/NetworkManager/NetworkManager.conf.
Add to the bottom of the file:
[device] wifi.scan-rand-mac-address=no
Save and run: systemctl restart NetworkManager