Thanks again. Your advice was very helpful - and I want to summarize for others who want to import contacts from older outlooks to nextcloud:
With your help I
- saved and imported the old .pst file
- installed a current version of outlook (this could be a trial version) and imported the old .pst
- choose the right .pst file under “Systemsteuerung” - “Mail” - “Datendateien” -> “…Documents…” not “…AppData…” as “Standard” (the old contacts appear at outlook when selecting the right ‘contacts’ on the left of the contacts-menu)
- installed “CalDav Synchronizer” in Outlook (Best way to migrate vom Outlook (Exchange) to Nextcloud?)
- here carefully selected the right “synchronization profile” with choosing the correct outlook-contact and calendar files (there could be more, hidden in the menu, due to the .pst imports)
- and carefully chose the “profiles” so to use the same path in nc and caldav
-> Finally all outlook contacts with every detail appear in the nextcloud contact app to be synchronized with other devices, so as smartphone or thunderbird on the laptop…
Great