if issues in safe mode too then nothing works as it might be software/ hardware issues. Visit service center and ask them to reflash firmware this is only thing you can do and if this also not works might be motherboard (hardware or battery) issue.
To resolve auto restart issue please follow below given steps:- Go to Settings > General management > Reset > Turn off auto start.
If the issue still persist kindly visit the service center for the physical inspection of your device. To check for the nearest Samsung service center kindly click on the link:- https://www.samsung.com/in/support/service-center/
