Explanation

John would force himself to work on till late in the night.

جان خود کو رات گئے تک کام کرنے پر مجبور کرتا۔

Here "Would" shows possibility.

"Would" is used to indicate a habitual action in the past.

"Could" implies ability, which does not fit the context of forcing oneself.

"Would be" is incorrect because "force" is a verb and does not require "be."