When the default game mode is changed, for example, the command block does this and the «World Options» tab is open, the default game mode will change, but this will not happen visually. Reproduce:
This can also be reproduced in a singleplayer world. First, give yourself a command block using the command: /give @s command_block
In Creative Mode, set it up and run a small chain of repeaters and put a button at the end.
Enter the command there: defaultgamemode creative
Open the world to the LAN.
Press on the button and go to the «World Options» tab. After the command block changes the default game mode, this will not happen visually on this tab.
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