Not everything, but it's incredibly easy to fall into something being an official act, and most things of consequences would end up there, especially if you're a corrupt president planning to use this ruling. There are a few constitutionally-defined acts that are 100% absolute immunity, but the ruling also gives a presumption of immunity to other official acts that are not defined. That's why they're sending it back to the lower court - to determine which acts were official. Which will then be appealed and affirmed and then appealed back to the Supreme Court. But by the time they have to grant immunity, the election will be over. They very much did not want to make a decision about what acts were official so they wouldn't have to make explicit that Trump is immune until after the election.