After upgrading from stretch to buster, I'm having this same / similar problem. The Alt+1/2/3/4... keys that used to work for switching windows don't work anymore. Interestingly, Alt+c works for closing the window. This is using Sakura terminal + screen.
I tried to change the X resources configuration as mentioned in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=348035 using xterm, but that did not work either. This is the first time I had to configure X resources, so not sure if I'm doing that correctly, but most likely yes. -- Sent with [ProtonMail](https://protonmail.com) Secure Email.
