The only issues I've ever had with upgrading Oracle versions was triggered by changes in Oracle.  For example, DBMS_OBFUSCATION_TOOLKIT get's deprecated and DBMS_CRYPTO needs to be used instead.  (https://oracle-base.com/articles/8i/data-encryption).  In another case, one of our developers decided to use an internal, not officially supported Oracle function called WM_CONCAT.  Great until Oracle eventually removed it (https://oracle-base.com/articles/misc/string-aggregation-techniques#wm_concat).  So it's a matter of reading through the Oracle docs to see what got removed between the version you're currently using (which you didn't mention) and 19c.    Also, you might migrate a test database to 19c, run through your application against it and see what breaks.  Good time to have something like AscentialTest (https://zeenyx.com/automated-testing-tool/) in place so that you can automate such end to end testing whenever considering upgrades like this.

PowerBuilder 2022 does support Oracle 19c.  However, the quality of PB 2022 R3 should be better and it has long-term support (at least 5 years).  So I would recommend rolling out your Oracle 19c upgrade together with the R3 long-term support version of PB 2022.