optimizer_features_enable in 19c

Hi,

Recently upgrade our database from 11g (11.2.04) to 19c (Version 19.8.0.0.0).

We had issues with the DB performance and set the optimizer_features_enable to 11.2.0.4

But this did not help and we switched optimizer_features_enable to 19.1.0

After humungous tuning effort, some stability was obtained where in many cases we had to pass the optimizer hint as 11.2.0.4 in a lot of queries with performance issues.

Some questions based on anyone's experience:

1. Does switching optimizer_features_enable to 11.2.0.4 and back to 19.1.0 causes any adverse effect for DB performance, had we never made the switch initially?

2. In 19c (19.8.0.0.0) do we have any better