There’s more information in the following post which details what you will need to do in order to continue with 1.8 Legacy. In short you will need to install 1.8 Legacy on your core and any desktop machines as well as the new 1.8 Legacy remote apps on your mobile devices.
There is no need to turn off auto updates for the mobile apps. Just install the new Roon 1.8 Legacy mobile apps an you will be on 1.8 until you elect to move.