The documentation for RunService:UnbindFromRenderStep()
states that
If there is no bound function by the given name, this method raises an error. You can prevent such an error from being raised by using pcall.
However, we can see that this is false by running
game:GetService("RunService"):UnbindFromRenderStep("foo")
from the command line, which does not throw.
Page URL: https://create.roblox.com/docs/reference/engine/classes/RunService#UnbindFromRenderStep