RMD for 1948-DOB owner's new retroactively adopted (or as yet unfunded) DB plan

So hey, what if there's a first, vested, accrual (in my case, a cash balance credit) as of 12/31/2020 for the owner and no money's been put in the plan by his RBD of 4-1-2021?

And does the answer change if the plan was adopted before the RBD, such that "we knew this would be due...."

(I expect the RMD to be paid via an in-service distribution of his entire benefit so that he can use the DC method, too, and roll the rest to his IRA.  That's got me thinking about an interest adjustment for the late payment, too.)

Any thoughts appreciated.  thanks.

Oh wait, am I okay since the 4-1 date would have been the 2020 RMD which was based on $0 accrued benefits, and then at some point in 2021  we adjust for the new 2020 accrual?  Getting my DB/DC RMDs swirling in my brain.

-bri