itunes deleted all my own music and videos from my iphone

Sorry for delay in replying, more lockdown issues, and some other reasons that I might expand about later if need too.

Anyways I think you may be replying to the wrong message as in mine I stated itunes deleted "all my own music and videos from my iphone 8, when using add to device and synch set to manual" as in boom, gone, bye bye, adious amigos, so not point really in "checking if the music was inadvertently removed" it was itunely deleted. And yes itunes is set to manually sync and heres another one for you .. next day then, i found that this amazing software done the same to my old iPhone in another room that I was just using as a music player .. I figured that out too, iTunes had flipn wirelessly connected, I didnt know that was possible with iTunes, to that phone and wiped at same time as new phone, great stuff there, really made me remember why i gave up using iTunes back in the day let alone try and understand it and I've worked in IT on major IT projects across the world for over 20 yrs now ... I never really used iTunes before for these type of reasons

So as it was lockdown and some time on hand I spent some lovely quality time with iTunes and my devices testing different sceanrios etc and I now know exactly in each 'setting' when iTunes deletes stuff. So iTunes makes its virtuall impossible foor me to manage my own media in the way I want to use across devices. I just dont get 'Apple Logic' , I know that most do so that just the way it is. So i bough some sofware and was able to sort all out devices again with a few clicks and my media backups from my backup drives. Thank you for trying to help anyways.