Yup, that's called a 'stevedore", always releases.

In article , Keith
wrote:

I don't know what it's called, but I make a stopper knot by making a bend in
the line, wrapping the bitter end around the standing part 3-4 times, then
passing the bitter end through the bend and tighten the whole thing up.
Works well, and can usually be undone fairly easily.