What is Deprecation of Non-CDB Architecture means

Please check the below link for point (8.1.1 : Deprecation of Non-CDB Architecture).

https://docs.oracle.com/database/121/UPGRD/deprecated.htm#BABDBCJI

"Deprecation" means "at some stage in future, Oracle *might* stop doing enhancements on this features, and at some stage after that, Oracle *might* no longer support it".

In 12.1.0.1.0 non-CDB (old architecture) is not deprecated whereas from 12.1.0.2.0 it got deprecated. Even if you have single database, it is better to have it in multitenant architecture as 1CDB and 1PDB.

As per Oracle document:- https://docs.oracle.com/en/database/oracle/oracle-database/12.2/upgrd/deprecated-features-oracle-database-12c-r2.html#GUID-5D181F03-F74D-4888-B7B2-7176CF6FA8F8

Deprecation of Non-CDB Architecture

The non-CDB architecture was deprecated in Oracle Database 12c. It can be desupported and unavailable in a release after Oracle Database 19c .

Oracle recommends use of the CDB architecture.

Oracle Database 19c ?

Release 12.2: New releases will be annual and the version will be the last two digits of the release year. The release originally planned as 12.2.0.2 will now be release 18c, and the release originally planned as 12.2.0.3 will be release 19c. Releases 18c and 19c will be treated as under the umbrella of 12.2 for Lifetime Support purposes. The current plan is for Oracle Database 19c to be the last release for 12.2. This may change in the future to Oracle 20 as the last release for 12.2