Adding new worksheet default cell format is time. How to set cell format of added worksheet standard

Hi,

if I add a new worksheet the cell format for all cells by default is time. This means, when I type a number e.g. "0" it will be displayed as 00:00:00

Searching the internet didn't bring a solution.

Once I remember I read about a bug with a certain hotkey combination containing "#".

But anyway what the root is: How and where can I set the default cell format for a new worksheet?

Btw. if I add a new workbook the cell format is standard. Even if I add a new worksheet there.

So it must be sth to adjust within the property of a workbook. Thanks in advance for your help!

Ch.