If you are on a Mac (apparently you are, using COMMAND-A), then the hotkey to call Command Palette is COMMAND-SHIFT-P). Alternatively Menu View / Command Palette...
Then you have to call actual Format Document command from there. The hotkey to call it directly is OPTION-SHIFT-F on my Mac.
I assume, you don’t need to install JuliaFormatter.jl on your own. In any case, I never did, and I have the working Format Document command on my Mac.