Upgraded to Office 2019 on my MAC (latest=10.15.1) - now word cannot open old word docs, or save new

Hi,

When upgrading my mac to latest OS (10.15.x), my old Office stopped working. Newest version needed. 

I went on a procured Office 2019 for Mac.

Installed it. Not a problem.

Starting excel, powerpoint or work not an issue.

1. In word - i cannot open old word doc's. I get error:

"The document “SPITSBERGEN EXPEDITIE 2019.docx” could not be opened. " It does not matter which document i try to open. Neither where the docs are located.

--> bonus info: I can open the docs with LibraOffice and with OpenOffice

2.. When i make a new document, everything works. But when trying to save i get doc i get: 

"The file “Desktop” couldn’t be opened." Desktop is the location i try to save to. It does not matter where on my mac i try to save the document - it does not work.

--> bonus info. I can save new docs with LibraOffice and with OpenOffice

Why don't this work out of the box with Office 2019. All previous upgrades of MS Office have given no problems. 

What do i have to do to get access to my existing office documents?

What do i have to do to save new docs made in Word 2019?

I know i can edit and update all documents via LibraOffice and OpenOffice - on my Mac. Why not with MS Office 2019?

Regards

Per