¶ Opening GUIs by Command
FancyMenu comes with a command that lets you open Vanilla and Custom GUIs via command.
You can even remotely open GUIs for other players when installing FancyMenu on both server and clients.
To open a GUI, just use the command /openguiscreen <screen_identifier> <target_player>.
Replace <screen_identifier> with the actual menu identifier of the GUI you want to open.
This can be the identifier of your Custom GUI (made with FancyMenu) or the normal menu identifier of a Vanilla/mod GUI.
To get the menu identifier of Vanilla/mod GUIs, open the menu you want to know the identifier of and enable FancyMenu's debug overlay via Customization -> Debug Overlay, then you can click on the identifier shown as first line to copy it to your clipboard.
Leave the <target_player> argument empty to open the GUI for your client or choose a player (or multiple players) to open the GUI for.
Keep in mind that the other player needs to have FancyMenu installed on their client.
¶ Closing GUIs by Command
In the rare case you need it, there's also a /closeguiscreen <target_player> command that closes the current screen.