Soldered RAM doesn't meaningfully affect laptop heat.

Negligible.

RAM uses very little power, whether soldered to the motherboard or in a replaceable SO-DIMM slot. The heat it generates is a rounding error compared to the CPU and GPU. If your laptop is hot, it’s the processor or graphics chip roasting, not the memory modules.

Some soldered RAM sits closer to the heatsink or heat pipes, but that doesn’t matter because there’s almost no heat to remove. The thermal performance difference between soldered and socketed RAM just isn’t a real-world factor in overall laptop temperature.

The real downside of soldered RAM is that you can’t upgrade or replace it. Heat is not the issue.