As above, try smashing the base first, you might find there isn’t a substantial lump there and then you can use the pole to free up most of it.
You could dig round it to see how much concrete is actually there. You’ve got to hope it was done on the cheap and whoever put it in used the absolute minimum.
As above dig round the pole to see how much cement there is. Had similar situation with a basket ball hoop installed on the drive of a house we bought, fortunately there wasn’t that much concrete. Dug it up whole then cut the pole, as above don’t cut the pole first as it could be useful for applying leverage.
I had four of those in my lawn, each one embedded in so much concrete it looked like Robert McAlpine himself had been using my garden to practice in. So they got cut off as low as possible, below grass level, and each one given a little grass toupee. Seems to be fine.
Having tied to break up the concrete on the base of one, I’d just dig it out. Have chopped off the top of one as a “last solution” option bar.. & had to use it on a stuck BB (two of us, one holding the frame and one using the bar eventually got it!)
I took one of those out for my folks, it was an easy sledgehammer job to break up the concrete, but then it was pretty low quality concrete. I am not a concretist, but yours doesn’t look that great either?
Just like everyone else I have nothing constructive to add. I removed something similar a few years ago. Started out thinking it was going to be fairly straightforward until I found that actually there was roughly the same amount below the surface. It was hard work.
You could try dropping a lit banger or three down the inside. Or maybe get it realy hot with a blowtorch so it expands and cracks the concrete, then coolit with iced water so you can pull it out.