The flow triggers the time zone we are in Europe/Berlin and I found our system timezone is:

Does that mean it's because of that? Is there another way to check for “On Tomorrow” without changing the time zone of the system?

Thank you for your help!

This could very well be the cause (it's checking on system time to determine what is 'tomorrow').

But since you are checking on knowledge articles to see if they are valid until tomorrow, what does the rest of the flow do? I think it's kind of a short timespan to do something with the articles if they are just valid until tomorrow, but it depends on what you are doing with it, of course.

If a KB article is valid until tomorrow we send a notification to the author to inform them. Do you have any suggestions to check on for tomorrow, because I can´t change the timezone fo the system.

I have now been able to test it and it is actually due to the system time zone. Thank you very much!