You don't have to root your device for debloating.
System apps can be "uninstalled" from adb shell
adb shell pm disable --user 0 <pkgname>
(actually that will disable the app. Do this again after each factory reset)
If your device is rooted with Magisk you can remove apps from system (overlay).
Just create some empty files for the file/...
With methods described below, when the phone disconnect from your wifi network, wifi will be immediately switched off. Also they don't require the Location Services to be on.
A. Xposed Edge
Open Xposed Edge, go to More triggers > Wifi Disconncted > Wifi > Turn off.
Open Macrodroid, click Add Macro.
Click the + on the right of Trigger. ...
If you have only 1 USB port in the PC, try a PCIe USB card.
As for rooting with Magisk without a PC, unless you can find a port of TWRP for it, I doubt it. (There's no official TWRP for the A20, and flashing Magisk requires TWRP as far as I can see from everything TopJohnWu has said. You can try the one at https://mega.nz/folder/LTZlUKyI#...