I use it all of the time.? I assume you are talking about direct keyboard text commands to the sBitx radio app.? If not disregard.
A typical UNIX type problem is the window needs to have focus first.? Have you tried clicking on the sBitx app and then hitting the "\" key?? That's the key to the right of the "]" key just above the "Enter" key on a US layout keyboard.? If you hit that key and the window doesn't have focus it won't work.
Commands I typically use are:
\low 400? ? ? ?(for SSB)
\low 0? ? ? ? ? ?(for SWL)?
\freq 10000? (for WWV)
AE9J