I had HS3 a few Years ago. I'm now trialing HS4.
I was wondering how to Log QSO's and send QSL Cards in HS4. It doesn't appear to work the same way as HS3. I can't see any Boxes to input the info in the Log Book.
I'm running it on a Laptop, with Linux Mint 19.3 Cinnamon.

Just click on the "Log Book" button and on the next page the yellow "Log Book" again.

Now you can enter all information about your QSO.
To send a card you have to create new QSL-Cards for HS 4 first.

73 and good DX from Jörg :-)
JO31ok
Bochum / Germany