Nintendo has announced on Twitter that the team is currently hard at work working on a forthcoming patch for Splatoon 3 which will fix a few issues players have encountered with the excellent game. Firstly they addressed the black screen issue which appears to happen for some users at the very start of the game just before you get the train into Splatsville. This temporary fix below does seem to solve the issue for the time being, until the patch is out.
1. Start the game without having your Switch connected to the internet (such as enabling airplane mode
2. Choose your character’s appearance, then proceed to Splatsville
3. Connect your Switch to the internet while in Splatsville
4. Enter the Lobby to transfer your save data and choose your Splatfest region
Nintendo also said that there will be other issues addressed in the forthcoming patch such as some of the disconnection errors players have encountered, especially when playing the Salmon Run mode. It is not clear when the update will be released, but clearly the sooner the better.