I have a Fairphone 3 running Android R. I also updated to version 1.3 and have the same experience :
In order to switch it on, I must keep the power button pressed for about 10 seconds.
Then the Fairphone logo appears, followed by the /e/ logo.
I can then input my sim code, and then unlock my phone with the requested pattern.
Then the phone can be used normally for about 15 seconds, before freezing its screen for 3 seconds and finally turning off. (Black screen).
The /e/ recovery can be accessed, as well as Fastboot mode.
The bootloader is locked.
I tried booting the phone with a SIM card and no SD card, without SIM card and with SD card, and without both : the problem still happens.
Would there be a way to solve this without having to unlock the bootloader (resulting in data loss), and flashing version 1.2 ?
Moreover, it will be really important to mention this when @Manoj posts the “version feedback” thread.