I didn't say a club can't do anything, I said no sensible club will want to do anything to force an unwilling manager to stay.
The manager is far more important than any player, so forcing them to stay would have a disastrous knock-on effect on morale and willingness to perform across the whole squad. The players would say to each other, "the gaffer wants out, so why should we walk through walls for him (and in any case he'll be gone soon enough)?"
And in any case, the club could no longer have confidence that the manager was doing their best for them - in terms of man-management, team selection, coaching and so on. It's just not practical.