How can I stop people from joining and taking stuff in Survival Mode?
Solution 1:
The only people who can join your world are people on the same network.
In the options, under Multiplayer, uncheck "Server visible by default". This will make any new worlds you make unjoinable.
Then, enter your world. Pause the game, and click the bottom button such that it says "Server is invisible". Ta-da!
Solution 2:
Or turn off wifi go to settings go to wifi and turn it off