Cannot Play or Save Game Due to In-game Windows not Opening
@yumekumo Just to be sure, you've tested new saves with no mods or custom content present? And are you playing in fullscreen, windowed mode, or both? If you've been using fullscreen mode, I'd try windowed before doing anything else.
If that doesn't help, please try playing in a clean boot:
The one service to leave enabled is the EABackgroundService, which the EA App needs in order to run. Disable the rest as described.
When you reboot your computer, go through the Task Manager's background processes list shutting down any service that doesn't absolutely need to be running, for example anything from MSI Afterburner to RGB software might still be enabled. If you accidentally kill a critical process and it doesn't restart on its own, just reboot your computer again.
Don't open anything other than Sims 4 and the EA App while testing, not even a browser window. I realize you may not want to play like this going forward, but it's a helpful test.
