Sloan Park will open for Cubs spring training next week at about 20-25 percent capacity, or somewhere around 3,500-3,750 fans (I’ve seen sources quote both numbers). Tickets are completely sold out for the 14 games scheduled.
It remains to be seen whether there will be fans permitted at Wrigley Field this year. As you know, I have been in favor of delaying the season, which as of now isn’t happening, and perhaps sometime in May for fans to be at the ballpark.
It is true that with COVID-19 caseloads dropping and people being vaccinated, some small number of fans at the two ballparks in Chicago could happen this year.