New roster rules for Major League Baseball teams in 2020 permit a 26th man to be carried from Opening Day through the end of August.
The rule change mandates that of the 26 men, only 13 can be pitchers. In recent years, most teams have done this and carried only 12 position players. Thus, the 26th man is almost certainly going to be a position player for most teams, including the Cubs.
The Cubs have several candidates, noted in this Tribune article by Mark Gonzales. Gonzales cites Ian Miller, Daniel Descalso, David Bote and Josh Phegley.