tl;dr I am using the same Apple account / AppleID on both my iPhone SE 2020 and iTunes for Windows 10. Yet, Windows version of iTunes does not see this iPhone among my devices and "Sync" menu item is disabled. What should I do to fix this problem?
I am using the same Apple ID in both iPhone and iTunes / Windows 10:
I have even authorised my PC within my account (not sure, if that was necessary):
And yet my iPhone is not among my devices. Actually, it seems that I don't have any device, because corresponding menu items are disabled:
As an effect, I cannot see these audiobooks in my iPhone, as they are not being synced up to that device.
What should I do fix this problem and get File > Devices > Sync menu item enabled?