New models integrate all the front IO into the motherboard, so they really only work with the case from the manufacturer. Like this and this.

A lot of things, yes, but not everything.

This is from iFixit:

Lenovo ThinkPad T14 Gen 3

2022

PROS
Most repairs are very straightforward and require only basic tools.
The keyboard replacement procedure is best in class.
CONS
Partially soldered memory and I/O ports hinder certain repairs.

It scores 7/10 on their repairability meter. Definitely not the best, but far from the worst.

Jesus, it'd be easier to list the parts you don't have to remove.

While I agree, it's hard to find a cheap and reliable laptop that's not a thinkpad. The keyboards have suffered and some of the models are harder to repair. But they're still spill proof, tough, and have lots of ports. I don't regret my thinkpad t14 gen 3 purchase. I might get a thinkpad t14 gen 2 soon.

They absolutely do not record keystrokes and phone that home. You’re talking about the Intel Management Engine, which is completely useless to almost everyone, but there’s no evidence that it spies on you. There have been security vulnerabilities found in it that could let someone else compromise your system (notably: only if you’ve provisioned Intel Standard Manageability), but there is practically zero chance that Intel is doing that or even selling that sort of capability.

How confident do you need to be? I don't think I've seen any convincing evidence of any firmware spying in PC components.

Well, except the NSA's Clipper chip, but I don't think that really ever got implemented.

Well you can find a list of Libreboot compatible hardware here. I feel like your biggest issue, especially if you are relying on a prebuilt Windows PC, is all the bloatware they come with on top of Windows itself.

Pay now or pay later.

Well ThinkPad back in the days weren't cheap either but then even a 2nd hand one could still last a while and one could still get them fixed.

There is no "budget option" if you value repairability, nor has there ever been. The best you can do is buy a secondhand ThinkPad or other workstation laptop. If you don't like that option, make more money.

I got my PC built for me by a local computer shop for $100. Worth it to me for the time it saved plus they did a 24 hour stress test on it to make sure all the components worked.

That only applies to a large corporation with contracts.

and upgradable

If it's not something that can go in a slot for Dell HP and Lenovo there is no upgrade. They aren't going to swap an upgraded CPU because Dell doesn't do official bios patches to upgrade old PC's to cpus that come out later. Nor can you get a new motherboard dropped in an old Dell/HP/Lenovo chassis because of the power supply requirements/changes.

Edit: I couldn't even put a modern GPU in my old Dell Xeon because the power supply didn't put out the watts. I had to find a weird Dell to ATX converter cable off of eBay and Dremel the Dell case a little so the regular ATX would fit.

The name is Gamers Nexus, not Corporate IT Nexus.