How to create a backup image (*.ab) of Android Device that is not booting up? I am just a usual android user, owning  9-10 android devices. My Mom's Android device automatically turned off yesterday and while booting up again, it was stuck in the company Logo  

and was not turning on. The device is "10.or E" exactly this  model. 
My Mom had some very important files in her phone storage that she cannot compromise with. So, she came to me and asked me if I could turn it on without losing her files. I tried turning the phone on using the combination of the three buttons together (Power Button + Volume Up + Volume Down Buttons). This didn't do any good but yeah, it was able to turn off the mobile. Then I tried to go to Recovery Mode (in this device it is done by the combination of Power Button and Volume Up button) and check if there is an option available for making full device backup like my another device. Unfortunately, there was no option to create a "Full system backup" on SD-Card. It had some other options. See these images:

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Now, as there was no option to create a full backup using only the concerned device, I opted for my PC to do the same. I have SDK(s) installed  of all the Android Versions form Lollipop to Android 10 (don't know it's name). I switched off the phone and connected it with my PC using USB-Cable (not sure if USB-Debugging was on or not). After connecting I tried to give the adb command for backup  but it could not establish the connection with the device. Whereas, in the list of my devices I see a device named as Qualcomm HS-USB QDLoader 9008 (COM5)  

which means that the device is detected by the computer. Although the device is detected by the computer, I am not able to create a backup using adb commands. 
I don't know any PC Backup method other than the sdk-cmd-adb method. 

So, as this is a very big problem because my Mom's Data is extremely important to her and she cannot afford to lose that data, I really need a working method to get her Android Device's Backup before flashing new firmware or Factory/Hard/Soft Reseting it. There are so many Android Enthusiasts over here that may also have faced this problem before or may face this problem in future so, if any of us could help me in this issue will not only be helpful to me but to all of the faithful Android Stack Exchange Members. 
Please help me, I am left with no other option.

Thank You So Much in Advance ❤️❤️❤️
The approach you are taking is not worth it for you simply because: 


USB debugging needs to be enabled beforehand for using any adb command on a device. Since your mother probably would have never felt (and why would she anyway?) the need to enable it, assume it to be disabled. 
Since debugging can only be enabled either manually by the user under Settings app, or by using a custom kernel, or by using a custom recovery to make changes in data partition, your chances of enabling it are zero. 
Even if debugging is enabled the two most important processes are either not started or not fully functioning for enabling and approving backup via adb. One is the activity manager which is required to seek approval for backup via UI, and the other is the backend backup service which nobody can tell (without logs) whether it is started or not because of the boot issue.


In short, dump this approach because it is futile and a waste of time in your case. All I can suggest is to find out a way to either load a custom recovery somehow without deleting userdata. I've never tried that, so that's all I can offer.

You can try looking for Qualcomm chipset flashing type tools. They may be able to help you load a custom recovery/kernel so that userdata partition can be accessed.   Beware with such tools though. They sometimes don't list partitions for selective partition flashing and flash every partition in wholesale, including data partition which is of prime importance here. Good luck!