I had the same problem. The phone shut down on itself a few minutes after every restart.
The timeframe was just long enough to install a hardware-checking-app. From the readings in the app I learned that an internal temperature sensor shows 90°C straigt. Even just after rebooting an login, despite I cooled it down to about 4°C the fidge before.
After removing the back cover, unscrewing all screws and finaly remoing the bezel, I managed to regain a true temperature reading by sligtly pushing an knocking the PCBs. Then I located the faulty sensor on the SUB-circuitboard next to the USB-connector by applying cold spray. Unfurtunately replacing the SUB-circuitboard has NOT fixed the issue.
To get the phone charged again I connected an USB-charger with was not plugged into the wall. Then i checked the temperature reading in the app and made it changing from fake 90° to real 27°-32°. Then I put down the Phone verry gently on something cushionlike to avoid disturbing the temperature mesaurement by vibrations. Then I and plugged the preconnected charger into the wall.
After reaching 85% I disconnected the USB-charger and the flexprint connector to the SUB-circuitboard. That disabeld the faulty temperature mesaurement, so I had not to expect the backup process beeing interupted by "safety shutdowns". Unconviniently also the USB is inoperable, when the flexprint is disconectet. So I culd not connect the Phone to my PC directly. Luckily the M32 features a µSD-card-socket.
I installed the app "SmartSwitch" and then inserted a card of 128Gb into the matching cutout of the SIM-tray. ThenI let "SmmartSwitch" saving everything to the µSD-card. It took over one hour (and a decent percentage of the battery charge) to copy everything, but wit the disconected sensor no inerruptions occured.
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