MacBook Pro (2017) motherboard replaced - Time Machine issues

Hi,

Recently my motherboard went off on MacBook Pro (2017). Had to replace with a new one.

I made a backup with Time Machine to a NAS server via internet connection.

Now I have my completely emtpy MacBook with the new motherboard, with the original op system (Sierra).

I updated it to Catalina.

Try to connect to the NAS. It's ok so far.

But it doesn't find my backup file. It's there.

How can I solve this?

Thanks a lot!