Export of Workflow yields files with knwf extension that cannot be opened

I have installed KNIME (v5.2.1) on my new computer. Now I want to export my workflows from the backup site to my local disk. The export produces files with the extension .knwf but those cannot be opened. I presume something with my settings is wrong. Did anybody encounter the same problem (and knows how to solve it)?

Your support is much appreciated.

Here is how I export.

and here is what I get:

The file ‘OldPackWeight.knwf’ has the expected extension. However, it does not have the KNIME icon and it does not open in KNIME.

Johannes