I should have discovered this years ago!
I never came across this feature, and it was apparently available a few versions ago. Just now, when version 25.12.0 was officially released, I learned how to simplify upgrading from one version to another (I did this from 24.10.2 to 25.12.0).
I have developed my own routine for backing up packages and configuration files, installing a new image, and restoring everything. To be honest, I always hate doing that, especially in a business environment, as it always requires some downtime. This is why I sometimes fall behind on some sub-versions of OpenWrt firmware (I was still on 24.10.2 instead of 24.10.5).
When you cannot afford extended downtime, you can minimise it with this approach: Attended Sysupgrade (ASU).