Hi,
I have the problem that I am not able to choose custom fields when I create a custom report.
Is it somehow possible to use them for custom reports or do I have to do this with SQL/SWQL ?
Yes you can choose the custom fields in report.See the below snapshot , you may choose IPAM Group Node attribute which Subnet Custom fields or IPAM IP node Attribute which is IP Address custom field.
The Problem now is that I could not choose the default fields for the report??
Columns can be selected based on entity(IPAM Group Node Attribute). If you need different columns from different Entity(other than IPAM Group node Attribute) then you need to select "Advance database query" method.Custom SWQL or custom sql may be good option.