What's the mandatory withholding?

Small payout to a beneficiary. No other assets distributed to this beneficiary before or after.

$416.23 gross amount in pretax Code 4 monies 

$425.03 gross Roth Code 4B monies of which $329.75 is basis ($85.28 in Roth earnings)

What's the mandatory withholding? Don't read anything fancy into the situation. It's just a basic, non-CARES Act related payout to a beneficiary.

Let me know if I've left out a pertinent fact, though. Thanks.

Depends- since the PPT is deceased, if the Designated Roth has satisfied the 5 year rule than nothing but if it hasn't satisfied the 5 year rule, then the earning are subject to withholding rules.