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I mean, depends how bad the lean is. I'd probably just fiddle with it a bit to stop the chair rolling around and you could maybe use a different thickness on one side if it's proper wonky.
You could also use that carpet underlay stuff and build up one side a bit more than the other and then cover it with your top layer (carpet mat, plastic mat, etc)
Could also change the orientation of your desk/chair so you roll towards the desk rather than sideways or whatever.
Interesting ... would you expect that to be functionally self levelling?