Straw man and Moving the goalposts both have useful meanings, but online, the more common definitions are:
Straw man: "I don't have an answer to that, so I'm declaring it irrelevant."
Goalpost moving: "I'm declaring I won, and you changed the terms."
The terms are used wrongly but sincerely by people whose belief systems prevent them from seeing what lies behind a facade and what the actual goals are.
ETA: second definition modified after comments below.