Dataminer OatmealDome reveals that Splatoon 3 uses NPLN for Lobby Features. For those not familiar, NPLN is the new server system developed by Nintendo which is a lot better than the previous system (NEX). NPLN is used in the lobby as it’d be difficult or impossible to implement its new features into NEX. NPLN is still relatively new, as Splatoon 3 marks the third game to use the system. NPLN only reached version 1.0.0 in Monster Hunter Rise.
It’s unknown if this applies to matches. OatmealDome has noted that it’s “likely still peer-to-peer (pia)” though we won’t know for certain until the game launches.
Additionally, OatmealDome reports that Nintendo is using AMD’s FidelityFX Super Resolution (FSR) 1.0 technology in Splatoon 3. It’s an older version of FSR that uses spatial upscaling, which upscales based on data from the current frame being displayed.