Hello there, thank you for writing to us! Could you try the following to see if it reproduces without old saves potentially causing any issues:
Go to "C:\Users\user.name\Documents\Paradox Interactive\Crusader Kings III" and move the save games folder out of it, verify your files and then launch the game again?
If that doesn't work, could you please zip up the "logs" folder that is found in the same file location as the save games, attach them here, as well as running the "DxDiag.exe", saving the information to a .txt file and uploading it to this thread.
Go to "C:\Users\user.name\Documents\Paradox Interactive\Crusader Kings III" and move the save games folder out of it, verify your files and then launch the game again?
If that doesn't work, could you please zip up the "logs" folder that is found in the same file location as the save games, attach them here, as well as running the "DxDiag.exe", saving the information to a .txt file and uploading it to this thread.