The lack of user replaceable batteries is one symptom of a larger problem, yes. And the symptom being discussed today.

Part of the issue with old smartphones and batteries is that every battery is a snowflake so eventually nobody is willing to produce the replacement battery anymore.

Contrast this to car batteries where the form factor is specified within certain limits.

This is, unfortunately, a point where the law probably has to step in and say "battery replacements must be available for 20 years" which would make it unpalatable to be a snowflake anymore. At that point, the suppliers would get together and agree on a "standard" battery form factor.

You are correct. without datasheets, you have no way to even approach reprogramming a computer system. Those datasheets, schemata, and documentation are some of the closest, most tightly held trade secrets in the tech world.

Increasingly, the world has gotten away from "sell thing to owner to own" to "sell hook for revenue extraction from User". part of which has also increasingly been "be the unofficial or unnoticed arm of power by keeping inconvenient things hard to acquire as determined by the parties in power". Say... industrial equipment without backdoors.

Until I can load my own firmware/microcode, it ain't mine yet. I'd love to have a cobbled together group of heterogenous computing devices just for the novelty.

And that’s the reason to continue to grow the FLOSS / Open Hardware ecosystem.

You don’t have to program or fix stuff yourself. But you should be able to hire your local shop to do it for you at reasonable expense and to keep your old, but good, stuff running as long as you like.

While flip phones are disposable are their price point, that’s not true for hardware like smart phones or beyond. We need better, sustainable solutions.

Smartphone software being pure garbage along with the games Qualcomm and the network operators play make up the rest of the story.