Here's his Insta announcement: https://www.instagram.com/postmalone/p/DCjp14mRn6G/?img_index=2. Says "Indio, CA" on the days of Coachella. I'm betting Post has to wait on announcing his European run of festivals until after the Coachella announcement.
Post Malone just announced his US tour today, ends July 1, so plenty of time to get over to Europe. He is also expected to announce a Coachella headlining slot, too. I bet that's why Sziget had to postpone the announcement, Coachella probably made Post do that. Still, having a proper Coachella headliner speaks well for Sziget. Hope @Sziget2025_Leaks is right, Post would be a big grab this year. https://pitchfork.com/news/post-malone-seems-to-leak-news-of-coachella-appearance-with-2025-tour-announcement/