The SSD is soldered onto the motherboard on all new apple laptops and has been for years, there is no replacing it without the whole board. Which can be 70% of the cost of a new laptop.
Whatever ram and SSD config you buy when new is how it will be forever.
This is the exact reason I am currently very uncomfortable with the idea of a new Macbook Pro for my own business use.
On the one had it absolutely makes life a lot easier and all the software I need runs great on it. On the other I would by buying into a device I simply cannot upgrade or maintain myself. This makes me extremely uncomfortable.
I dont want to run Windows as a daily driver since it is really jarring for my personal workflow etc. Yet Linux lacks quite a few of the essential pieces of software I need outside of development. E.g. (Krisp.AI, Reincubate Camo etc)
For as often as I've had to upgrade a machine, or had a hardware failure, I'd just choose whatever works best for my daily workflow. An inconvenient fix that takes my computer out of service for a day while I run over to the Apple Store that only happens every few years at most is just not comparable to something that puts a drag on my workflow every single day.
I was a windows user and thought the same thing for awhile about switching to Linux. I was heavily dependent on Adobe products to create PDF Forms. Then I realized I could use a CRM solution to handle the from creation for me. I wrote about my experience in switching to Linux and so far it is work well for me: https://www.scottrlarson.com/publications/publication-transi...
Have you replaced SSD's because of failure or to upgrade? I personally have never seen an internal SSD fail. My 2018 MacBook Pro has had zero issues, and I still use a Samsung Evo 840 SSD from 2013 in one of my PCs.
I'm not agreeing with Apple soldering the SSD to the logic board. But they do seem to be significantly more reliable than hard drives.
Anecdotally, I did have a Samsung T5 go tits up on me not long ago. But that's an external drive. Not from physical abuse, either, it spent its life sitting on my desk.
I've never had any kind of problem with internal SSDs.
Usually to upgrade capacity, but I have had one personal SSD fail (I've used... 30? 35? in the last decade). It was an internal drive, 60 GB OCZ bought in 2012, failed in 2015.
Similar here - 256GB 830 Pro, lasted damn close to a decade and was in my desktop, then my sons and finally my daughters before it died. Very high writes as well - it was a great SSD.
Whatever ram and SSD config you buy when new is how it will be forever.