Major increase in transaction log backup size after upgrading to SQL Server 2022

This is not uncommon, it has been seen after upgrading to SQL Server 2022. Even if the workload hasn’t changed, SQL Server 2022 introduces a few features that can increase the amount of transaction log activity. One of the biggest contributors is that Query Store is enabled by default on upgraded databases, and that alone can noticeably increase logging overhead unless it’s tuned or disabled. The newer persistent log buffer and changes in how the engine flushes and optimizes writes can also generate more log traffic, especially in Always On environments, since more data is being flushed and replicated more efficiently. Finally, because your new hardware has higher throughput, it’s likely completing more writes in the same time window so the log backups look larger simply because SQL Server can push more work through. In short, nothing is “wrong,” but a combination of new engine behavior plus Query Store plus better Input Output can easily explain the 3x to 5× change. If needed, tuning Query Store or adjusting backup/log settings can help bring it down.