I always hear about how modern laptops and smartphones “aren’t repairable” and then I spent a week in Shenzhen.. where there were floors and floors of independent repair people doing specialized fixes to the most intricate parts. I had an old Apple Watch repair for about $20, only to discover that I got ripped off — I could have negotiated it down to much less.
Apple and others put in a lot of effort to stop independent repair shops from sourcing original parts or making them impossible to successfully replace due to hardware DRM. It is already impossible to upgrade some Macs with more RAM because they will simply refuse to boot if they find more RAM than they got in the factory.