Quorum Queues are a superior replacement for Classic Mirrored Queues that were introduced in RabbitMQ version 3.8. And there are two complementary reasons why you would need to migrate.
First of all, Classic Mirrored Queues were deprecated in 3.9, with a formal announcement posted on August 21, 2021. They will be removed entirely in 4.0
But also they are more reliable and predictable, faster for most workloads and require less maintenance - so you shouldn’t feel that your hand is being forced without no apparent reason.
Quorum Queues are better in all regards, but they are not 100%-compatible feature-wise with Mirrored Queues. Thus the migration can look like a daunting task.
After a sneak peek into the future performance improvements, this post outlines a few possible migration strategies and includes guidance on how to deal with incompatible features. The Migrate your RabbitMQ Mirrored Classic Queues to Quorum Queues documentation is also available to help you through the migration process.