First of all thanks to the community for the quick attempts to help me out.
However, undoubtedly it is also a smart feature to create a seed and so on before you initially use the Wallet. But when I first downloaded / used Jaxx, this security feature wasn't obviously standard, so I didn't have to do that :-/
I didn't understand this part of your post. What do you mean that it wasn't standard? I am not sure how exactly Jaxx displays the seed, but you should have seen a copy of your 12 words seed sometimes during the wallet creation process. It was never displayed to you, or did you not write down a copy of it? Jaxx is a horrible wallet, security-wise, but I believe they still let you make a copy of your seed
I am sorry if my explanation was insufficient. According to my BTC-Record it was Aug 2019 when I transferred the BTC to my Jaxx Wallet. And I strongly guess it wasn't very long before that, that I installed the App for the first time. And I am pretty sure that, unlike now, it was not the case that you were first asked to create a seed - You could start right away with the creation of the wallet and that was it. The "standard" to call you to write up a seed, must have been - according to my experience - established somewhen after Aug 2019. That's at least my strong guess.
So the answer in short is: It was never displayed to me, because I never knew and searched for it after I installed the App initially and transferred coins on it.
From time to time I had a look into the wallet and never saw any significant change. Also, since Aug 2019, there have of course been a lot of updates of the iOS and -most likely- the Jaxx-App as well. However, I never had a so deep look into the wallet, that I saw something like 'ah, you need to do a backup from your seed or private key'. I guess I thought the wallet was connected with my Apple-ID so I could restore it anywhere, also if my phone was stolen or lost or something just by using the latest backup on my harddrive or iCloud. With other apps it is working also like that (for example I wasn't even asked to long in to my twitter or LinkedIn App. It was a different story with my Banking-Apps -_-). But that wasn't obvious the case.
>>snip<<
First thing to always do before sending your Bitcoins to an address is to first make multiple backups of the wallet including copying the seed and keeping it in a very secure and safe location. Encrypting the wallet file a lone and leaving it in the device isn't enough as the you can easily lose the mobile device anytime.
Yes - lessons learned definitely for now.
I doubt whether you will have the wallet file in your backup, thou the wallet app itself could easily be restored. The other alternative would be not to install any app or copy any media into the phone and use a recovery software to first recovery all the deleted files and folders then locate the wallet file. But this is a long shot and might not be worth it.
If this is a serious option - what software would that be or is there anywhere a tutorial how to or something? As I said initially: I can't imagine that I am the first one with this specific problem.
Thank you and best regards
SD