Is it possible to use backup data from the 2019 version of SharePoint and restore it to the 2016 version?
Or is there any other way to downgrade from 2019 to the 2016 version?
No, it isn't possible. The only supported way would be to use a migration tool such as Sharegate.
Restore from a newer version to an older version is called Backward compatibility that not supported in SharePoint as well as SQL Server.
Only Forward Compatibility is supported. otherwise, you will need to use a 3rd party migration tool to can restore to an earlier version.
It is not supported by Microsoft. We are not able to downgrade a SharePoint Farm through a supported approach.