UPDATED 6/29:
As things stand right now...
63 Cubs minor leaguers are eligible for selection in the December 2021 MLB Rule 5 Draft, and 52 Cubs minor leaguers (37 post-2021 6YFA and 15 2021 second-contract players) are eligible to be declared MLB Rule 9 (formerly known as 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).
In addition, C-INF Tony Wolters was assigned outright to the minors on 5/22 and OF Nick Martini was assigned outright to the minors on 6/7, and because Martini has Article XX-D status (Martini has been outrighted previously in his career) they had the right to elect free-agency, or else defer the right to elect free-agency until after the conclusion of the MLB regular season (he had 48 hours to decide), and because Wolters has Article XIX-A status (he has accrued at least five years of MLB Service Time) he had to give his consent before he could be outrighted and once outrighted he had the right to elect free-agency, or else defer his right to elect free-agency until after the conclusion of the World Series (he had 48 hours to decide).