I had e/OS installed by a IT specialist. I wonder if one can make a backup (like with an Iphone and Itunes). In other words, if for any reason the mobile needs a fresh install can I put back a backup of everything? Otherwise I have to ask a specialist every time a new install is needed which is gonna be expensive.
Regain your privacy! Adopt /e/ the unGoogled mobile OS and online services
Welcome to the community, dear @eosfan.
Updates that are sent to your device OTA and you are going to be notified about are safe to perform by yourself as the instructions guide you. No data shall be lost.
Major updates between Android # (10 → 11, P → Q) are safer with partition formatting. You can find the device specific instruction/manual following Smartphone Selector Doing so, taking backup is strongly recommended. Upgrades require some advanced user skills, but read through the manual and judge yourself.
There is a TWRP recovery commands to backup and restore the content of the whole device (except media and download, see further). It may be possible to backup and restore selectively only user data (photos, documents, downloads, etc.), but I do not recommend to do it between major updates. Plus, we know nothing about your Recovery partition. E.g., e-recovery has no such options.
I would separate the ‘everything’ into user data, applications’ and OS settings. User data you can backup via USB connection by connecting your device to a computer. These you can safely copy back after the upgrade.
OS settings is not transferable, to my knowledge.
Apps may have their own import and export options, but not all. If they do not have one, transferring settings is not trivial and I consider it not possible.
I recommend to try backing up and saving as much relevant data as you would wish to restore later – just as a practice. Write a list about it. Extend the list over the next week, when using the device. I personally forgot quite some data at the first major restore 
“user data (photos, documents, downloads, etc.)” is exactly the stuff TWRP does not backup … What is EXCLUDED from a TWRP backup?
TWRP does not backup the whole device without some trickery.
Not in a totally convenient manner. One of the weakest points of Android.
An example of what can be done …
… but the unlocked bootloader is a trade-off with security implications.
The /e/OS developers are working on integrating Seedvault into /e/OS, which will help, but it will not be a perfect solution either, as it has its limitations, too.
Backup
Restore
ADB backup sports a “deprecated” label for a while now, and restore doesn’t work 100% conveniently or even reliably, if you want to believe the internet (and my practical experience).
Apart from the fact that ADB backup doesn’t backup the OS, so not the whole phone.
From Android 12 on, it seems it’s almost game over …
adb backup has never worked satisfactorily in /e/ (or any other recent custom ROM that I know of)
The Android Backup and Restore Tools project looks promising. Trying it out has been on my To-Do list for a while. If you have access to a Linux PC, then it may be worth a try
Thank you very much Yopixi.
Thank you very much for taking the time to explains matters in detail. As you understand I am new to e/OS and not into spending weeks trying to figure out IT problems like I used to be 20 years ago ;-). So tanks a lot!