Soldered RAM runs hotter under sustained load.

Yes, it does.

Soldered RAM is crammed right next to the CPU with minimal airflow and often no heatsink at all. Replaceable SODIMMs sit in a slot with some air gap and usually have a metal shield or even a thermal pad. Under a render that pegs everything, that difference shows.

It’s not a dealbreaker for most people. A laptop throttling from soldered RAM heat is pretty rare unless you’re pushing a thin chassis with high-end specs for hours. But if you’re doing sustained renders or machine learning, the extra headroom from replaceable RAM (or a well-ventilated soldered design) matters.

Check reviews that show sustained thermal loads, not just benchmarks.

Your render will finish either way. The soldered machine might just take a few percent longer.