How do I stop loops using another script?

What I did was make a Boolean value so a script could interact with another. But how can I use that to my advantage in stopping a while true do script in the middle of the piece of code at any point in time?

You're explicitly stating that something should only done while this is true, so that means you shouldn't be using a while true loop, you should be using an actual condition:

while someCondition do
	-- (your loop)
end

Alternatively, as M39a9am3R suggested, you could use a break to emulate this:

while true do
	if not someCondition then
		break -- Stop the loop ("break" the loop)
	end
	-- (your loop)
end

you can stop it by using another script and putting a Bool Value in the script thats going to stop it. Have the script change it by doing script.stop.Value = true or what ever you want it to be.

Then in the one you want to stop, just add this to the top

if not game.Workspace.stopScript.stop.Value then
while true do
	--stuff
end
end