Hi Nikolas,
The default one is mapped to the field “Company Name” in Lead entity, whose data type is “Single Line of Text”.
If you’d like to use the form to register an event, it will create or update your contacts. So it is necessary to map the form field to the field of Contact entity, whose data type is Lookup.
Of course, if you just want to use the form field in a Marketing Form to update your leads only, the default one is enough for you.

If this helped you, I'd appreciate it if you'd mark this as a Verified Answer, which may in turn help others as well.
Best Regards,
Nya