In the Default Magento2 Marketplace module, there is no option for an extended signup form for seller registration.
However, if you want to integrate this feature into your Marketplace then you can install the Marketplace add-on Magento2 Vendor Attribute Manager.
This module allows the admin to create vendor’s custom attributes. Vendors can fill the attributes on the registration page and can update these attributes on the vendor profile page.
Please do contact us for any further queries or requirements. You can also check our Magento 2 Extensions for additional features.