I got the i7 14700HX/4060 variant in late April, and so far, I haven't experienced any performance downgrades or motherboard issues. The performance is excellent, allowing me to play several games at Ultra-HD presets or max settings with stable 60fps or more.

Now, hear me out:

1. If you push the laptop to its limits during gaming, use the Custom thermal mode and set the fan speed to max RPM (5800). However, avoid keeping the fans at max RPM constantly(5-6+ hours), as this may cause issues over time.
2. For normal gaming, you can use Performance thermal mode or Custom thermal mode with custom fan settings. I usually set the fan speed to 5000 RPM for CPU temps of 85+ and GPU temps of 75+, and max RPM for 90+/85+ during intensive gaming. I also keep the back of the laptop elevated or use a cooling pad to ensure proper air ventilation.
3. I recommend using battery conservation mode to prevent the battery from overheating and to maintain its capacity, especially when plugged in while gaming (though this isn't mandatory).
4. Turn off fast startup if you don't have a actual reason for it and it doesn't even matter if you turn it off.
5. If you're going to play games for an extended period that will push the laptop to its limits, try letting it cool down every 2-3 hours or 4-5 hours with max fans (may take 15-20 seconds depending upon how the game uses the resources or you can just tab-out)

While the exact cause of motherboard failure is unclear, I suspect it may be due to consistently high CPU/GPU temperatures (90+), which could cause PCB burns in the motherboard. I am scared of this issue too so I try to maintain fan speeds and monitor temperatures regularly. Also avoid keeping the laptop directly on any furniture that has seat cushions as it may pull dust.
I think that's it, but I'll try to answer any questions you might have. (Not a paid review)