If you're running Mariko you're not really going to have any issues. We've had some discussions on what the temps could be, but on my own switch lite (the smoke clear Switch lite posted above in this thread). I run my switch lite 24/7 at 1.7ghz cpu, 921mhz gpu, and 1600mhz memory clock.
The highest temperature I've ever been able to observe is 50.x°C. I've never hit 51°C as the fan will ramp up to the high 30's% and will keep the chip hovering around this temp. (Using Xenoblade Chronicles Definitive Edition as testing. I'll probably install the 60fps mod at some point to try and ramp up the temps even more if possible).
Even at 50, let's say something happens and I get it up to 60°C, it's still WELL below the temp at which the chip starts throttling. IIRC it's 83°C it starts throttling. With a tjmax of 90°C.
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