MacBook Air models prior to the very latest may have their SSDs replaced. See here:I have a more simple and prosaic complaint: I would perhaps have replaced my family MacBook Airs (or is that MacBooks Air?) with newer computers some time ago, if they came with larger SSDs at a reasonable price, or allowed me to replace or insert an NVME drive.
I know from experience that the 128gig is too small for my uses, and 256gig barely enough. Apple may be proud that their SSDs are super-fast, but I'd be happy with the speed of standard NVME sticks. And right now, as it has been for ages, larger drives are still far too expensive.