No modern laptop lets you solder on extra RAM chips.

Not really. The idea of unpopulated solder pads you can fill later with a soldering iron—that died with the ultrabook revolution around 2012. Today, if a laptop uses soldered RAM, the pads are either fully populated or left empty because the motherboard was designed for a different SKU. Those empty pads are not for you; they’re for the factory to produce a cheaper version of the same board. Adding chips later requires BGA rework, matching firmware tables, and usually a hot air station you don’t own.

What you actually want is a laptop with upgradeable RAM slots. The Framework laptop is the closest thing to what you’re asking—it uses standard DDR5 SODIMM modules, not solder pads. Some business laptops (older ThinkPads, certain Dell Latitudes) have one soldered stick and one slot. But if you see unpopulated pads on a motherboard photo, that’s a trap.

Buy the RAM you need upfront, or buy a laptop with sockets. Resoldering DRAM is not a weekend project.