Old Skype 6.x in Win10 is forced to get a new interface "muzzle" (from Skype 7.x). How to counter this?

Question

Skype

One of the reasons why users are reluctant to switch to updated versions of Skype 7.x is the new user interface - white and blue, completely disgusting, devoid of many familiar features and therefore inconvenient to use. Those who want to stay on older versions of Skype have to fight with the auto-update built into Skype. Many people manage to win this fight ( including me ). But with the advent of Windows 10, elements of the new Skype 7.x once again break through the erected barriers. However, see for yourself.
This is how the old Skype 6.18 looks in Win8.1 :

All interface elements are in place and work in the usual way. And like this - in Win10 :

The old one had an instant message history line - "Show messages: Yesterday - 7 days - 30 days - 3 months - 6 months". The new one is missing. The old one had a "Submit" button, which means that the Enter key could be used to work with the text of the message, i.e. for its intended purpose. The new "Send" does not, so Enter must be assigned to send the message. There are other, smaller troubles, because of which this white-and-blue abomination wants to be abandoned.
Switching to Win10, I did not immediately pay attention to the change in Skype's face, but when I did, I made an attempt to return: I deleted Skype and installed the same version again. The old "muzzle" did not return. I deleted Skype again, after which I cleaned the system partition from files and folders with a name containing the word skype, and the registry from keys containing this word. It did nothing. Again I cleaned both the system and the registry, now as carefully as possible - it did not help. What could be the issue here? How does the "ten" manage (at least partially - only in the sense of the interface) to bypass those protection measures that normally work in the "eight"? And most importantly - how to resist it? In general, I ask "the help of the audience."