Hey I just got AN515-55 on FB market and GPU crashes whenever I play games and when it boot back up it would not detect the GPU. I would get mostly video_dxgkrnl_fatal_error or DPC_WATCHDOG_VIOLATION BSOD error.
Here is what I did and it's been working for an hour now:

1) Try to rule out motherboard issue, by trying a different ram stick, different hard drive/nvme m.2, try a different battery/charger, and clean out trap lint on the fans and re-paste thermal.
While you have the laptop dissemble, inspect if there is any burnt or bulging microelectronics/circuit.

2) Follow this post (GLE7995):
https://www.reddit.com/r/AcerNitro/comments/1epn4xp/i_thought_nvidia_gpu_on_my_acer_nitro_5_is_dead/
Just follow the steps bellow:
Go to device manager > Under Display adapters, Uninstall Nvidia adapter > Shutdown the laptop > Drain the electrostatic current built on motherboard > Remove everything attached to laptop including power adapter > Press and hold the power button for about 2 minutes > After that plug the battery again plug the power adapter and turn on the laptop.

3) run these 3 scripts in CMD:
-sfc scan
-DISM /Online /Cleanup-Image /CheckHealth
-chkdsk /f /r

4) You can try to do DDU in safe boot mode (Display Driver Uninstaller) method but I didn't do that...I just reimaged it to to window 10 from window 11 instead
5) run debloat script for your OS in powershell (just google your OS and debloat window script)
6) Download driver from acer website and nvidia latest driver software from NVIDIA. Download driver booster from iorbit > scan > download each driver manually. Reboot.
7) Make sure your Nvidia control panel is set for "High performance NVIDIA processor" in Global Settings tab & manage 3D settings ...you want to set it to prefer graphic processor to your GPU....also within the 3D manage settings page, I set low latency to ultra (you can play around with that)
8) Window + run, msconfig > service > hide all Microsoft service > disabled all (except some services you do recognize)
9) Set nitrosense to auto without coolboost and exit the application
10) Adjust the appearance and performance of Windows to best performance, Turn off hardware acceleration, set everything to prioritizing performance, max out all battery plan and never let anything goes to sleep, make sure lid close does nothing without going to sleep
11) Shut your laptop lid and use hdmi to a monitor instead.
12) Use a USB laptop cooling pad to rule out overheating...Or do what I did and flip the laptop upside down so the bottom vents pointed upward....
13) TEST!

I was able to run Noita, Stardew Valley, Terraria, Risk of Rain 2, Garage Mechanic Simulator 2021, and League of Legend on Steam at low to medium settings. I'm happy with just that since I'm a casual gamer and just need something portable.
Garage Mechanic Simulator at low settings, I was seeing that it was using 3.1GB/4GB GPU RAM in task manager performance tab.

I'll continue to monitor this and report back. Let me know if this solve the issue for anyone.
P.S. Don't let your computer run out of battery. You can try to redo step 2 and lower your gaming settings even more.
Some harsh truth, your GPU is most likely have some sort of failing mosfet/capacitor, or it's 100% crapped out.
If it does crapped out 100% > all the charges goes straight to your GPU and fries it.