As The Goldbergs showed in the Season 4 finale, Lainey is headed off to college in Savannah, Georgia, and won’t be around while Barry remains in high school.
Considering her character will be far away, it seems logical that AJ Michalka’s role has been reduced ahead of Season 5, although there’s still a chance of Lainey appearing at points throughout the season.
Executive producer and Stephen King fan Adam F. Goldberg tells TVLine that Michalka has been present for some table reads for episodes in the upcoming season, so it’s not as though the show is writing her off completely.