How can I set the configuration that the price that will be set in the admin catalogus is including tax and not excluding tax?
Could you please clarify your question?
I think this is what you're searching for:
Go to "Stores > Configuration > Sales > Tax" , then you should be able to find "Calculation Settings" and finally the option "Catalog Prices".
That option sets whether catalog prices entered from Magento Admin include tax or not.