M1 Mac RAM and storage can be upgraded after purchase, but it's not easy - 9to5Mac
OWC 16GB (2x8GB) ram Upgrade PC3-12800 DDR3L 1600MHz sodimm 204 Pin CL11 Memory Upgrade Kit Compatible with Late iMac, Mac Mini, and MacBook Pro Computer at Amazon.com
MacBook Air 13" Early 2017 SSD Upgrade to NVMe - iFixit Repair Guide
MacBook Air RAM Upgrade: What You Need to Know
M1 Mac RAM and SSD Upgrades Found to Be Possible After Purchase - MacRumors
13-inch MacBook Air (Mid 2012)
MacBook Air Teardown Reveals M2 Chip and Single Storage Chip for 256GB Model - MacRumors
How to upgrade the RAM on the new 2018 Mac mini | AppleInsider