The Keychron software is only for loading a config to the keyboard, or pulling a config for backup. The entire config lives on the keyboard after that.
You only have to use it temporarily while making changes to the keyboard, it's not running or connected beyond that, and isn't required at all if you don't want to change anything.
You can also use VIA (also online but only when needed) with Keychron, but I've not had much success lately with it.
You can also just download the firmware source files, and then modify, build, and install the firmware locally without ever connecting to the internet.
As an old: You kids and your TeamSpeak .. back in my day Ventrilo, and we were happy to have it! (uphill both ways or something about my lawn).