Re: MacOS 10.15 - Catalina
Thank you for posting and welcome to the community. I would be happy to assist with this.
The reason there is a step included for creating an empty .app folder is because iTunes no longer exists within Catalina, it has been replaced with Apple Music.
When adding a music library the SoundTouch app does look for the iTunes app as part of its authentication process and by having the .app folder, this tricks SoundTouch into thinking iTunes is installed for it to use.
Those setting it asking you to check under 'iTunes warning' is part of the original process to add the library directly from iTunes. With the workaround instructions you have been following, this setting change will not be necessary.
I hope this helps. Let me know if you have any further questions.