"This environment contains a previous version Common Data Service database.The previous version Common Data Service Database is being discontinued. Unless the upgrade to the new version is completed, apps and flows that store data in this database will stop working as these databases are being taken offline. Apps and flows that do not use this database are not affected.Learn more. "
Based on the thought you menitoned above, I think you have some misunderstanding on the upgrade process of CDS in PowerApps.
Actually, when you upgraded your previous CDS (CDS 1.0), the previous version Common Data Service Database would not be discontinued. The existing database (on the previous version of CDS) remains as is; there are no changes made to it.
In addition, Apps and flows connecting to the existing database (on the previous version of CDS) continue to work without any interruption.
Please check and see if the following article would help in your scenario: