SQL Server 2019 performance worse than 2012... am I missing something?
I believe you have just discovered why the recommended upgrade process is to to upgrade your database, enable the Query Store, and test before increasing the database compatibility level.

Change the Database Compatibility Level and use the Query Store
If you have a lot of plan regressions you can keep using the older cardinality estimator at the higher database compatibility level with:
ALTER DATABASE SCOPED CONFIGURATION
SET LEGACY_CARDINALITY_ESTIMATION = ON;