@Winfried Can you provide a screenshot or some further explanation on that?
This option was never available on FP2 under Androis 5 or 6 and I cannot find it in Android 7 either, at least not under FP OS and as described here.
The advanced mode just gives the possibility to do a full install of the current OS (in contrast to the incremental installs in standard mode that were available in Android 6).
Afaik this option to easily switch from FP OS to FP Open using Updater is just a myth.
Anyone please feel free to prove me wrong, I would be happy to learn.