Gravity updates for the clients if you change it on the server so it should affects everything
If you set the gravity on the client you can change the gravity for a single player (which affects all the stuff they have network ownership of, like characters), though the OP wants everyone’s gravity to change
true and 20 is the same as 20 and false and 20 is the same as false
Your code should work, try looking at the gravity in the properties window while the game is running. I’m pretty sure some other code is changing the gravity back to the default.
If the gravity is incorrect in the properties window, try adding print statements to section of you code that set the gravity back to the default and see which is causing the problem.
It would work changing it from a local script. I’ve done it before. But as you said, you want it to change for everyone so a local script is out of mind.