Version 5.5.1 (Splatoon 2)
From Inkipedia, the Splatoon wiki
Version 5.5.1 is an update for Splatoon 2 that was released on 15 November 2022 at 01:00 UTC. 
Fixes and adjustments
- Several issues were addressed for gameplay purposes.
- This update was the first update for Splatoon 2 after the release of Splatoon 3.
- This update was part of a series of updates pushed by Nintendo to a number of Switch games on 15 November 2022, with the same patch note, all of which are games that had long since stopped receiving updates months to years prior. ARMS (last updated 2018), Super Mario Maker 2 (last updated 2020), Splatoon 2 (last updated 2021), and Animal Crossing: New Horizons (last updated February 2022) all received this update.
- It is believed this update may have been released to fix a major security bug in a code component common between the games.