This bug affects two of my computers, a desktop workstation connected via Ethernet and a laptop connected via Wi-Fi. When I updated the computers, I didn't pay close enough attention to what Apt was doing until it had already removed Network Manager. I was able to reinstall Network Manager on the workstation as follows:
sudo sh -c 'echo nameserver 8.8.8.8 > /etc/resolv.conf' sudo apt install wpasupplicant=2:2.9.0-21 sudo apt install network-manager-gnome sudo apt-mark hold wpasupplicant=2:2.9.0-21 2:2.9.0-21 is the current non-backports version of wpasupplicant for Bullseye. Since Wi-Fi wasn't working on the laptop, I plugged a USB flash drive into the workstation, changed to the directory where the USB flash drive was mounted, and downloaded the required packages using this command: apt download \ network-manager \ network-manager-gnome \ wpasupplicant \ libbluetooth3 \ libndp0 \ libteamdctl0 I then moved the USB flash drive to the laptop, changed to the directory where the USB flash drive was mounted, and ran these commands: sudo dpkg -i *.deb sudo apt-mark hold wpasupplicant=2:2.9.0-21 At that point Network Manager was working again on both computers. Once this issue is resolved, the hold on wpasupplicant can be removed by running: sudo apt-mark unhold wpasupplicant
