How to start a bootlooping phone in Safe Mode
Sorry for the disappointing news, but there is no way to boot into safe mode without USB debugging enabled and already authorized by Android, and  root access or a custom recovery.

The content of the file named persist.sys.safemode must be set to 1 for the device to boot into safe mode. The file is located under /data/property, is  owned by root user and is part of root group only. If only the root privileges are granted, the file can be edited.