What you can do with an internal SSD module from a vintage Mac
In 2010, Apple started to release Macs with solid-state drives (SSDs) that used a socket and—with varying amounts of effort—could be removed and upgraded by the owner or by an Apple or third-party technician. But starting in 2016, nearly every Mac released has the SSD soldered directly to the motherboard. The iMac is a notable exception, but see the note at the end of this article.
If you have a Mac of the proper vintage, it can be from vanishingly easy to exceedingly difficult to get the “blade”-style SSD out of the Mac and replace it with a higher-capacity model. These blades plug into a slot, something like RAM but with a narrower connector. Apple developed multiple, proprietary connectors across its use of blade SSDs. In my wife’s recently purchased 2014 MacBook Pro, nothing is easily serviceable except for the SSD, which is a cinch to access, remove, and replace.