Rockstar insider Tez2 announced on X that players can't start planning GTA Online Diamond Casino Heist. He mentioned that Rockstar temporarily stopped this feature on PC to fix a serious problem. The good news is that players using PS4, PS5, Xbox One, and Xbox Series X|S can still plan it without any issues.
It's quite disappointing to witness the Diamond Casino Heist being removed from the game for a while. Yet, Rockstar might need to release an update that players have to download, and that could take some time. Luckily, the current event week doesn't have any special bonuses tied to it. Also, they disabled setting up an Arcade property as part of their efforts to fix the problem of cheating.
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The exploit in question seems to allow hackers to manipulate GTA Online accounts on the PC version, including unauthorized removal of money and making other significant alterations. Additionally, it can extend to taking remote control of the victim's PC, granting the hackers full access. Several players on the GTA Forums have reported experiencing such incidents this week.
Playing in closed sessions, like invite-only lobbies, is completely safe from this exploit. It's hoped that all sessions will now be secure, especially since The Diamond Casino Heist planning has been disabled.
After the casino heist and arcade setup were disabled, Rockstar Games published a GTA Online PC Temporary Change FAQs section on their support site. If you have any lingering concerns about the issue, you can refer to the site for detailed answers and clarification.