As part of a DL Vacation package I purchased for JFK-ZRH-JFK (MC outbound, PS return with an immediate UPG to D1 using a GUC) for Feb. 2022.
For JFK-ZRH C+ was fully "occupied" except for 2 seats, I chose one of them

; the center section of PS is all "X" except the first row; MC is nearly all "X" with 10 seats occupied, D1 has lots of selectable seats @$3000

.
Doing a "dummy/ingognito" booking for the same dates as my booked itn, 1/2 of the "X" seats I see on the DL APP in MC are BLUE.