Is it possible to update slash command string options every time the command is ran?
This command acquires data from Firebase and use it as string choices. However, data from Firebase is not constant and will change from the moment the slash command is registered.
Solution
1. No, commands are registered at the Discord API level. No this is not a Sapphire or DiscordJS limitation, it just just how the Discord API handles slash commands. 2. Instead of pre-defining options you should use auto completion which can be filled dynamically, for example try using /pokedex from @Dragonite which also queries an API for its options.