from the MSSQL vendor: https://learn.microsoft.com/en-us/sql/t-sql/statements/restore-statements-transact-sql?view=sql-server-2016

 Note: No SQL Server backup can be restored to an earlier version of SQL Server than the version on which the backup was created.

Thanks Ledoesp but we used to do restore earlier and it is changed something newly, I read the document and it says Backups of master, model and msdb that were created by using an earlier version of SQL Server cannot be restored by SQL Server. and we are trying to restore a user created DB. will that wont work ?  

just had a chat with commvault chat support and they said restore will work from SQL 2016  to SQL 2012 but they dont have any document which is stating the statement. little confused now. will wait for your update ledoesp. 

I think the note from Microsoft makes reference to any type of database, user or system.

If you search there are many queries related with this specific topic in Internet.

Additionally this is documented here: 

https://documentation.commvault.com/2022e/expert/61536_sql_restore_options_general.html

Note: SQL Server databases can be restored to servers with similar or higher SQL Server versions installed on it.

oh that means it can be restored from sql 2012 to sql 2016 but not sql 2016 to 2012 ? am i correct. 

you are correct. to higher version yes but not to lower version

Thanks Mate!