Upgrade iodéOS from v2.15 to 4.9

Hello everyone,
I’ve just checked the phone from my mother in law. She runs iodeOS for years.
All of the OTA Updates went smoothly.
Today I saw, that she is not receiving any updates since September 2023.
Looking at the github releases page, I see that there is version 4.9 available.

Before doing a quick job through flashing v4.9 through recovery
I’d like to ask, what is the recommended way to upgrade from 2.15 to 4.9?
Backup all Apps + data (NeoBackup or migrate-NG), reformat data and system, flash v4.9, reinstall all apps
is there a seamless way that allows to upgrade to v4.9 directly?