How to make a player unable to take damage?

So Ive been searching the web for about half an hour and I cant seem to find anything. I was wondeing if anyone knew how to enable and disable immortality?

Have you tried force shield?

https://developer.roblox.com/en-us/api-reference/class/ForceField

Or try locking the health value in a variable and when health changes, turn the health to that value again (and disable death).

Try using the Changed event:

local immortalityEnabled = true

game.Players.PlayerAdded:Connect(function(player)
	local CharHumanoid = player.Character
	if immortalityEnabled then
		CarHumanoid.Changed:Connect(function(property)
			if property == "Health" then
				CharHumanoid.Health = 100
			end
		end	
	end)
end)

I hope this helps!