I checked the box on the opening splash screen and now it closes automatically. Is there a way to change it back, so the splas screen stays after opening krita?

Go to edit/resources/open resources folder, close krita, then go up, up, enter the 'config' folder, open kritarc in a text editor and find the following text:

[SplashScreen]
HideSplashAfterStartup=true

Either change true to false, or remove it completely

Thanks a lot for your super-quick response!

Pure accident