These are great questions and like the others I'm not sure there is an answer to most, but I believe that if you can find your way to making the distribution (a) the amount is includible in the participant's income, whether they cash the check or not, and (b) you can withhold the default amount if they have not made a withholding election. See Rev. Rul. 2019-19.
Since the plan is required to comply with 401(a)(9), in the absence of more specific language, I would probably advise distributing the smallest amount that could be distributed under any of the benefit options and then periodically sending the participant a letter that they can elect a different election and the actuarial value of the distributions already made will reduce the amount available for distribution after the election.