UPDATED 9/14
As things stand right now...
60 Cubs minor leaguers are eligible for selection in the December 2021 MLB Rule 5 Draft, and 45 Cubs minor leaguers (29 post-2021 6YFA and 16 2021 second-contract players) are eligible to be declared MLB Rule 9 (formerly known as MLB Rule 55) minor league free-agents 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, INF Andrew Romine was assigned outright to the minors on 9/8, and because he has Article XIX-A status (he has accrued at least five years of MLB Service Time) he had the right to elect free-agency upon being outrighted, or else accept the outright assignment and defer the right to elect free-agency until after the conclusion of the MLB regular season (he had 48 hours to decide).