Running the commands you gave me shows red text saying I don't have permission to run this command. This is because your world does not have cheats enabled. To enable them temporarily, simply pause the game (esc), click on the big Open to LAN button, click on Allow Cheats, and finally click on Start LAN world. Then run the commands. You can disable cheats and close the LAN server by exiting the world (and then entering).
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"Are you falling asleep in the middle of my fascinating explanation?" - Qibli
"I can't even dignify that with a snort." - Winter