Retirement tax questions

IF that's going to be the situation for 2020, I guess they could also leave the RMD choice line in that follow-up page, but not allow it to be selected,  with a parenthetical "( No RMDs required in 2020 ) "  after it so everyone understands why it's not selectable.

 

......but now  I wonder how the partial RMD selection line works...or doesn't work ? 

____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*