Can we directly upgrade Oracle 12.1 to 19 c or do we need to upgrade 12.1 to 12.2 first and then 19c Can we directly upgrade Oracle 12.1 to 19 c or do we need to upgrade 12.1 to 12.2 first and then 19c, and when 19c will be available for download
The term used by Oracle is "direct upgrade". You have to take into consideration if your database is a multitenant (CDB) database. 

From https://mikedietrichde.com/2018/12/14/premier-support-extension-for-oracle-19c-and-more/ :


  Oracle 12.2.0.1, Oracle 18c and Oracle 19c all together sail under the cover of the “Oracle 12.2 Release Family” and hence have a common support frame


So direct upgrade should be available with the following versions: 11.2.0.3, 11.2.0.4, 12.1.0.1, 12.1.0.2, 12.2.0.1

I'm not adding the MOS support hyperlinks since if you are posting the question here I'm guessing you dont have a MOS account.