Soldered RAM cannot be upgraded — period.

If the RAM is soldered, it’s locked in. You can’t swap it for dual-rank, single-rank, or anything else.

The question assumes you can choose between different RAM configurations, but soldered RAM is literally glued to the motherboard. It’s not a DIMM slot. There’s no swapping. What you buy is what you get.

Some laptops have a combination of soldered RAM and one slot. In that case, you can add a module but you can’t replace the soldered portion. Dual-rank vs. single-rank performance differences are tiny anyway — usually 2-5% in real workloads. Not worth worrying about unless you’re benchmarking for fun.

If performance matters, buy a laptop with socketed RAM from the start. Soldered RAM is a tradeoff for thinness and cost. You don’t get to upgrade later. Know that going in.