I am Jonas and i can repair computers, sewing machines, a jawbone big jambox speaker, iphones 5 & 6, rc cars, neato xv-21 automatic vacuum cleaner, vacuums, etc
I would recommend unplugging the charger and battery then pressing and holding the power button for 10 seconds then pressing and holding the power button while plugging in the charger and then quickly release and press the power button. If this works then it might be something with the charger.
Thank you, can you try powering on the computer while holding Command and S on the keyboard until it stops at a prompt and then enter nvram fa4ce28d-b62f-4c99-9cc3-6815686e30f9:gpu-power-prefs=%01%00%00%00 and then type reboot? There is another solution for fixing GPU failure, there is only two issues with this fix which is brightness control doesn’t work (and may be fixed in the future) and mini DisplayPort doesn’t work because it connects to the dGPU https://computeco.de/Demux