3 Things to Know About Soldered RAM in MacBook Airs
Soldered RAM predates Apple Silicon The 2018 Retina MacBook Air already had soldered LPDDR3 RAM, proving Apple locked down upgrades years before the M-series chips.
Your RAM choice is permanent Whether you pick 8GB or 16GB, that configuration is fixed from day one. There is no way to upgrade later.
Buy what you need upfront If you think you might need more memory, get it at purchase. You cannot add or swap RAM after the fact.