Yes, all the above is very confusing. Also spend hours and then I got it solved (RTFM). :devil: :unhappysweat:
A1) Old Phone must have a working SD-card with enough empty space (yes, I have to mention it).
- WhatsApp and NOT be installed on SD-card and BACKUP is DONE to SD-Card.
- "www dot whatsapp dot com/faq/search/?q=SC%20Card&p=false"
A2) Do the WhatsApp Backup -> ...more, settings, chat & calls, backup (takes a couple of seconds for +-2000 chats)
A3) Connect WP to PC with USB cable - go to "SD Card" - you should see "WP\SD Card\WinPhoneBackup with backup folders"
You can check the Date/Time Settings (connect/disconnect as with my Win10-14251 the WP folder is NOT auto updated)
A4) Copy the "WinPhoneBackup" Folder to your PC / One Drive (external BackUp) :grin:
B1) WhatsApp is NOT installed on New Phone
B2) New Phone must have working SD-card (I did not swap the SD-cards between phones)

B3) Copy the "WinPhoneBackup" Folder to your PC / One Drive (external BackUp)
B4) Install WhatsApp (will give Error if "install new apps to SD" is set) - lucky prompt to override.
B5) Select "Restore from BackUp", then type your Display Name
Hopefully yours will also be successful.
Praise the Lord.