SteamCMD does not have a "list all" command to get all command options within SteamCMD.
Instead you have to use
This script outputs all the commands available and saves it to a file.
You can get the output without using the script.
GitHub Actions checks daily for updates and posts them to this repo. So this list will always be up-to-date.
Simply download the script and run it.
wget https://raw.githubusercontent.com/dgibbs64/SteamCMD-Commands-List/master/steamcmd_commands.sh; chmod +x steamcmd_commands.sh; ./steamcmd_commands.sh