How to stop a couroutine from outside of it, without the same coroutine yielding?

You may have to implement this without coroutines.

For example, if your coroutine ran a loop that happened every 0.5 seconds, you could instead just call a function that had this same loop (inside of a spawn if you needed a separate thread). Then, that loop could check if it should still be running before every iteration. You shouldn't need the spawn if the loop only starts and stops when a certain event fires.

local Running = false

local function RunLoop()
	Running = true
	spawn(function()
		while Running do
			print("loop has run")
			wait(0.5)
		end
	end)
end

RunLoop()
wait(5)
Running = false --stops the loop

However, if you do it this way, a problem arises. If the loop's wait time is longer than the time it takes to stop and start the loop again, it will start a double loop, printing twice every iteration. So to solve this, you should only need a debounce.

local Running = false
local LoopDebounce = true

local function RunLoop()
	if not LoopDebounce then return end
	LoopDebounce = false
	Running = true
	spawn(function()
		while Running do
			print("loop has run")
			wait(0.5)
		end
	end)
	LoopDebounce = true
end

RunLoop()
wait(5)
Running = false --stops the loop
wait(3)
RunLoop()
wait(0.25) --wait time that is shorter than loop wait time now does not create duplicate loops
Running = false

Hope this helps!