Are you really suggesting that Macs, in general, are non upgradable? Well, I guess I could have been wrong, but I was so certain that I was using an upgradable tower back in the day, and that was a Mac tower. I mean, you seem so sure that you know what you’re talking about, that Macs can’t be upgraded (RAM, HD, PCI-GPUs).
Can you upgrade your Mac Studio, Mac mini, iMac, or MacBook line? No, and if you can, marginally. Can you upgrade a Mac Pro? Yes, with limited options.
In an attempt to find some comity in this argument, you are both right.
During the Intel era, Macs were reasonably upgradable. I've owned four Mac minis, and I did upgrades to each of them. I replaced the hard drive and memory in the PPC unit, then both of those, along the CPU, in the first Intel model, then the memory again in a 2011 mini, and now I've added an eGPU and replaced the RAM in my 2018 Mac mini.
That's all in the past. With the move to Apple Silicon, the Mac is now much more a black box, hidden within untold wizardry and driven by fell magic. Apple isn't locking down the Mac to be mean, they are doing it because of the substantial benefits it provides. It gives all of the components of the SoC, such as the CPU and GPU, equal access to the high-speed on-package system memory. It reduces complexity by putting the SSD controller and other logic on-board. It significantly reduces latency because data doesn't need to be shuttled around from different components on the motherboard. That also means fewer points of failure that might require warranty service. This is the implementation of Apple's historical vertical integration strategy that Steve Jobs could have only dreamed of for the Mac.
There are real, tangible benefits to the consumer, and fits in with Apple's business model and engineering philosophy. The downside is that we can no longer replace various components, but system upgrades are already a niche market done by us nerds, and the benefits outweigh losing that capability, even for those of us who have done that in the past.