Is there a good reason to create an additional table to realize a 1:N relation?
even though I would not need it.

No. If you add it without any expectation of needing it, then it only serves to:

Add overhead when querying the data
Add overhead when adding or updating data
Cause confusion for other people working on the DB
Be a potential source of inconsistent data and other bugs

On the other hand if you think it is likely that there will be a need for the relationships to become many-to-many in future, for instance a line item being on multiple invoices due to partial payments or refunds, then there may be a case for adding the extra structure now to save on refactoring effort later but I would be wary of adding it from the start because of the above reasons unless I was very sure it was going to be needed at some point soon.
If you do add the extra structure but don't want to allow many-to-many to be a thing just yet, you have extra work to define constraints that enforce the desired one-to-many behaviour until it is no longer needed.