It is not just Nintendo Switch Sports that has received an update tonight. Around the same time that the game was updated, Nintendo also launched a new update for Mario Strikers: Battle League. As with Nintendo Switch Sports, this update is the first one to follow a major content update that came out near the end of 2022.
Once you update Mario Strikers: Battle League, the game should be at version 1.3.1. As for the patch notes, they don’t say much. All Nintendo says is that they “fixed an issue in which Rainbow-colored ? Blocks would not appear during Strikers Club Season Matches”.