Upgrading soldered RAM voids the warranty on anything you break.

It depends on the manufacturer, but generally any modification to soldered components voids the warranty on the affected parts, and often the entire laptop. You are not swapping an SO-DIMM; you are desoldering and resoldering chips on the motherboard. That is a board-level repair that most manufacturers explicitly prohibit.

Some companies (like Apple or Dell) will void the entire laptop warranty if they detect unauthorized soldering. Others might only deny a claim on the motherboard but still cover the screen or keyboard. The problem is you rarely know until you file a claim, and they will look for evidence of tampering. Even if you do a clean job, they can tell.

Realistically, if you have to ask, do not do it. Buy a laptop with the RAM you need from the start or one with upgradeable slots. Soldered RAM upgrades are for experienced microsoldering hobbyists, not the average user who just wants to save a few hundred bucks.

Future You will be happier with a warranty intact.