Aaron Bertrand explains why it’s probably a good idea to enable indirect checkpoints:
At Stack Overflow, the upgrade to SQL Server 2019 was not as smooth as expected. It introduced long recovery times and high CPU on a secondary, during synchronization activity after failover, patching, and network connectivity testing. This symptom wasn’t present during similar activities and workloads under SQL Server 2017.
Aaron points out that if you have databased created in older versions of SQL Server, enabling indirect checkpoints can provide a performance boost to certain activities around log writing., including backup times.