Hi,
I’ve also just taken the leap to e/os on a s10e. Just flash S build (android 12) you’ll just need to unlock your bootloader. I’ve encountered some issues woth GPS though (no galileo, multiple gps apps not working here).
As for whatsapp do a local backup in the settings then save internal/android/media/com.whatsapp to an external storage. Then after you install e/os copy it back where it where before opening whatsapp and it will prompt you to restore the local backup on first use 