Batch processing
Batch processing breaks a large sync into chunks so it cannot time out halfway through. Instead of one request trying to move everything, the job is queued and worked through in pieces, with progress reported as it goes. You can leave the page and come back to it.
A job is Pending, Processing, Completed, or Failed, and a job that partly failed reports completed with errors rather than a plain success. Failed jobs can be retried, and a retry resumes from where the job stopped instead of starting again. Old job records are pruned automatically after about a week.
On multisite there are network-level screens for the batch dashboard, jobs, schedules, settings, and activity, so a network admin can see and manage work across subsites in one place. Element-level batching goes one level finer and processes individual Bricks elements rather than whole templates, which is what makes very large templates practical. It is driven mainly from WP-CLI.