An important note about Cubase 13 and Key Commands

Cubase saves the key commands' configuration to a configuration file, which the plugin reads to get information about available key commands.

Up to and including Cubase 12, this configuration file was updated when you closed the Key Commands window in Cubase.

In Cubase 13, this file isn't updated until you quit Cubase.

It's important to note that this configuration file is the sole source of information for the plugin regarding key commands. If it's not updated, the plugin will remain unaware of any changes made to the key commands.

So, unfortunately, you must restart Cubase 13 after making changes to the key commands; otherwise, the plugin will be unaware of these changes.

I do not have Nuendo, but I presume the same applies to Nuendo 13.