Tried uninstalling PSPC_SDK from compatdata folder, reverifying, then launching again. This got rid of the error message that my Playstation SDK version was out of date, but did not let me in.

I don't have the full game, but I was trying to get the Guest Pass to work, which has all the same steps as the full version to at least log in and start playing, which is where I got stuck.

This error comes from the game not being able to read DLLs related to Playstation's SDK files, and is due to the fact that the game needs you to log into a PSN account.

Unfortunately, unlike God of War, which has a Steam Deck mode built in that lets you bypass this, or like Ghosts of Tsushima, where you can workaround it and play in offline mode, this game is completely online and completely requires the account.