*** No longer supported *** [RELEASE] Resilient My Ecobee Devices and ecosystem V6- migrated to custom capabilities & automation (presence, comfort settings, and more)!

Hi, everything is explained at the ST community wiki (under supported features and use case #1). For your use cases, you have to remove your remote sensors participation in the Night’s comfort settings and configure the ones you wish to use instead in the zoning smartapp.
https://thingsthataresmart.wiki/index.php?title=EcobeeSetZoneWithSchedule#Supported_Features

About your concerns about the ST classic mobile app, I believe that SmartThings will not totally shut down the ST classic mobile app as Smartthings itself relies on it for any hubAction related DTHs (Device Type Handlers).

All custom DTHs rely on the ST classic mobile app for the moment…

I’m also following the CLI thread, and hopefully, there will be a migration path for the custom DTHs.

Regards.