Will this work?

Sadly, I can't test this in Studio's Play Solo, since we can not chat there.

What this code is meant to do is, if someone wants to go BRB/AFK, then they chat a certain phrase that should continuously make them jump until they say "I'm back" to stop the jumping and return them to normal.

BRBMode = false
game.Players.LocalPlayer.Chatted:connect(function(msg)
	if msg == "I'll BRB" then
		BRBMode = true
	elseif msg == "I'm Back" then
		BRBMode = false
	end
end)

while BRBMode == true do --Did I do this correctly?
	game.Players.LocalPlayer.Character.Humanoid.Jump = true
	wait()
end

This might be more efficient

--when going brb
Instance.new("ForceField" game.Players.LocalPlayer.Character) -- Creates a ForceField for the player, Instance.new allies you to create items.
--Coming back from AFK
for I,v in pairs(game.Players.LocalPlayer.Character:GetChildren()) do --Fetches all items in the player
if v:IsA("ForceField") then --sees if any object is the ForceField we made
v:Destroy()
end
end