List of server commands/gamemode
From Vintage Story Wiki
/gamemode [0..4|guest|survival|creative|spectator]
Mode names can be shortened to any length. Sets your game mode:0|guest
Guest mode - Cannot place/remove any blocks but can interact with them1|survival
Survival mode - Can slowly break/place blocks. Can die. Cannot fly. Survival inventory.2|creative
Creative mode - Access to all blocks through the creative inventory. Instant block breaking. Cannot die. Can fly.3|spectator
Spectator mode - Cannot place/remove blocks and cannot interact with anything, but can fly.
/gamemode [playername] [0..4]
Sets the gamemode for given player.