Hero 5 had still ambarella whereas the hero 6 has a Socionext Gp1 Soc....I would tend to think that if sofwtare says it hero 5 should be still with amba ....weird "prototype"
probably unbrickable... https://gopro.com/help/articles/Solutions_Troubleshooting/HERO5-Black-Will-Not-Power-On
"If there's no response, attempt to reset camera by pressing and holding the Mode Button for 8-10 seconds. After releasing the button, leave the camera alone for ≈5 seconds and attempt to get a response from the camera by pressing the Mode Button"