As noted, this is a freewheel. They get as tight as the leverage of the large sprocket, the hills and the rider's legs make possible. Removing them requires the same kind of force.
IME, the easiest way is to place the wheel and remover in a vise, channel the spirit of Ralph Cramden, and take your bus through a hard left turn (without power steering).
If you don't have a vise, but do have a long wrench, fill the tire, and stand wheel between the wall and floor with the freewheel to the left. Arrange the wheel and wrench so you'll be pushing toward where the baseboard. Your weight on the wrench will jam the wheel tighter so it can't spin, and the freewheel will come off.
BTW- the wall/floor method is very effective, allowing you to put all your strength into the wrench, but arrange yourself so if/when the freewheel pops loose you don't tumble head first into the wall.
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FB
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