UPDATED 4/12:
As things stand right now...
72 Cubs minor leaguers are eligible for selection in the December 2021 MLB Rule 5 Draft, and 51 Cubs minor leaguers (46 post-2021 6YFA and five 2021 second-contract players) are eligible to be declared MLB Rule 55 minor league 6YFA at 5 PM Eastern on the 5th day after the final game of the 2021 World Series (or at 5 PM Eastern on October 15th if the 2021 World Series is cancelled).
Among the Cubs first-time Rule 5 Draft eligibles post-2021 are RHPs Riley Thompson, Cam Sanders, Jeremiah Estrada, Ethan Roberts, Yovanny Cruz, Manuel Espinoza, Eduarniel Nunez, and Benjamin Rodriguez, LHP Jack Patterson, 1B Shendrik Apostel, 1B-OF Alfonso Rivas, INFs Luis Verdugo, Andy Weber, Luis Vazquez, Yeison Santana, and Fabian Pertuz, and OF Nelson Velazquez.