This extended version (GitHub) of Simple Contacts Pro (F-Droid, GitHub) supports separate address fields for post office box, apartment/suite, street, city, zip code, state and country name.
The extension makes the app compliant with other applications (e. g. Thunderbird with CardBook, iOS Contacts) and cloud services (e. g. Nextcloud) that support the CardDAV and vCard standards (RFC 6352, RFC 6350).
To activate the new feature, go to settings and select "Structured Addresses (edit mode)" in Manage shown contact fields dialog. When active, the combined multiline address field in contact editor will be replaced by a set of individual fields for address components.