Let me tell you a little anecdote. Our pickup truck used to be a 1977 Ford F-250, with a 5.8L eight cylinder engine, and a big carburetor on top. The engine made only 160HP (meaning top speed on flat ground was ~70mph, and in the hills I often had to drop to 20mph uphill, which makes the people driving behind me very unhappy), and fuel consumption was about 8-9 mpg (meaning the truck cost me a fortune in gasoline). Running it in idle for longer than 10 minutes caused it to overheat (mechanical cooling fan). We did most of the maintenance ourselves, because it was easy: The engine was uncomplicated (there was I think exactly one transistor in it, in the ignition), there was lots of room in the engine compartment (matter-of-fact, sitting on the fenders you could dangle you legs between the engine and the wheels), and generic parts were available everywhere. If the engine didn't run well, or something was broken, I could adjust or replace things myself. I often spent an hour on the weekend inside the engine compartment. Also, the trucks electrical system was trivial: There was a battery and an alternator, and a lot of manual switches in the dashboard, with wires that lead to things. Upgrading or repairing the electrical system was tedious but easy, and parts could be found at any store.
We have since replaced it with two new trucks. One is a 2007 Dodge 2500, which has a 5.7L eight cylinder engine, fuel injected and computer controlled. It can make 365HP, which means I can actually drive on a freeway at speeds that don't annoy other people, and I can responsibly bring 5 tons of gravel home without becoming a road hazard. And on flat ground, it uses only 18mpg, so it is hugely more efficient. The second is a 2005 International diesel, with an electronically injected 7.4L engine. It makes a near-infinite amount of torque (which is needed, the truck weighs 25,000 pounds), and you can run it all day long at low RPM to operate hydraulic systems. But: Maintenance on these trucks is nearly impossible for an amateur. The electrical systems are mostly computerized; matter-of-fact, to add extra functionality (like new safety lights) you need to get a Windows laptop and a $800/year software package, but you don't need to add switches or wires, because the dashboard is already full of electronically connected switches, and there are remote power controllers in all the right places. The manufacturer actually gives away the manual for adding functionality to the electrical system, except that the manual is about 450 pages long. Doing engine maintenance would be nearly impossible for an amateur, since the engines are computer controlled and exceedingly complex. All I do is filter cleaning and oil changes, the rest is left to very skilled and highly paid people.
See a pattern here? Both new trucks are MUCH MUCH better than the old one. They have much more power, they are much more reliable (the Dodge has never had an engine problem, and that's after 14 years of heavy use), they are much more efficient, and they do the job much better. If you can get help from skilled people (for example the dealer that has the laptop with the software package), they are easy and efficient to adapt to new tasks. The way the manufacturers (both Chrysler-Dodge and Navistar-International) achieved this is to add complexity, miniaturization, and computer control. The price that is paid is that repairs and upgrades by unskilled amateurs are no longer sensible, and in some cases de-facto impossible. It's not that the manufacturers make maintenance/modification impossible. On the contrary, I've spent an hour on the phone with Navistar-International tech support, and they explained exactly how remote power distribution works, how to program the system (if only I had the laptop, wire harness and software), and where to get the $300 specialized connector and harness to plug in.
Well what makes me more wonder is this: Apple isn't exactly building most of their products with repairability by the end user in mind.
Correct. They build products that are feature rich, efficient, compact, reliable, and good to use. Products that delight the user. Repairability is designed around a workflow that involves highly trained repair people, replacement of large integrated units (like whole boards), and expensive tools and jigs. Have you ever wondered why modern computers are no longer screwed together but glued, and why all chips are soldered to the board instead of in sockets? That's because screws and sockets are larger, heavier, less reliable, and generally the opposite of what you want in a small/powerful/reliable product.
In fact the opposite, they are gluing stuff in, putting traps in by which the device can detect it has been repaired "unauthorised" and they do wall even their hardware so much, that when buying two iPhones for example with the exactly the same configuration, and you are exchanging cameras between these two iOS will already complain and shut down features.
False. Worse than false, paranoid delusional. You seem to think that Apple (and by extension much of industry) is out to get you, they're trying to hurt your interests, trying to cheat you, part of a giant conspiracy. No, cell phone manufacturers are nothing like that. There are good and logical reasons for each of the things you complain about.
Glue? Lighter, smaller, stronger, and more reliable than screws.
Unauthorized opening? Look, a device like a cell phone or laptop is "trusted" (study the technology for TCB sometimes). When I plug my 2FA device into the phones USB socket, the software can detect that the path from the CPU to the 2FA is trusted, because nobody can have modified the hardware (since opening would have been detected), and a MiM attack outside would be detected in the protocol. Once sealed and secured, opening (or more accurately reclosing) can only be performed by authenticated and trusted partners.
Have you ever talked to people who build high-performance audio and optics? Cell phone cameras (and microphones these days) are calibrated, and the calibration is stored in the phone. If you switch the camera hardware between two phones, it will not work as well as one should expect, since now there is a miscalibration. And that calibration is not easy to perform at home; I know that for audio, they use anechoic chambers with sound generators (cameras must be similar). A friend of mine (a real musician, with an electrical engineering degree) works for a cell phone manufacturer (hint: Apple headquarters is 15 miles from my house, Google not much further), and when Covid started and he had to work from home, he took several $100K worth of testing and calibration equipment from his lab home, because that's what needed to work on cell phones (he doesn't repair customer shipped once, he tests and modified pre-production prototypes, but that's the same concept). Are you goin go buy $100K worth of logic and spectrum analyzers, just so you can replace parts of your phone?
will they ... build their stuff more repairable again?
If they did, 99.9% of customers would refuse to buy it. It would be bulky, weak, and fail all the time. For the same reason as: If Ford still offered the 1977 model of pickup truck, nobody would want it, because it is super underpowered, unreliable, and inefficient. If you want an antique that's easy to work on, there are suppliers that cater to it. For example, one of my neighbors drives and repairs a 1958 Thunderbird convertible. But not every day on the way to work, that would be insane.