[2023] Ever since the 3.9 update I can't play Stellaris. it just crashes immediately every time I try to open it and play

Game updates can make the game and the launcher a little wonky, unfortunately. There are several things you can try to fix this issue, try each of these steps in order, and attempt to load the game after each one:
1. Disable all mods
2. Verify Local Files (Steam) - Right Click Stellaris, Right Click Properties, Go to Local Files and click ""Verify Integrity of Game Files""
3. In the launcher, go to Settings, and change your Video Settings to Borderless Fullscreen or Windowed mode
4. (In Windows) Go to Settings, Add/Remove Programs, and Uninstall Paradox Launcher v2. After relaunching the game, let the launcher download updates, and restart the game again.

If none of these things work, go to support.paradoxplaza.com and open a ticket. Customer Support will be able to help you sort things out!