The 2019 version of Skype will always automatically log you in when you start Windows, and there's no way to quit it!

Take these steps to prevent this. You only need to do it once.

1) Go to the search bar on the bottom left and type: Windows Powershell

2) Right click on the Windows Powershell suggestion and select "Run as Administrator"

3) At the prompt in the powershell, enter: Get-AppxPackage Microsoft.SkypeApp | Remove-AppxPackage

That's it!

This removes the "Skype App" from Windows 10, and allows you to only run the desktop version.