As far as I can see, the T440p is the latest Thinkpad to support Coreboot/skulls.
If I wanted something newer (say, something from 2019-2022 or so) under $400, what could I even get? I want to run my own choice of linux distribution on it, so most chromebooks are out of the question (also I'd like something more powerful and upgradeable).
Ah, the problem here is my budget. I'm trying not to spend too much (preferably under $400) and at this point perhaps a T440p might just be decent enough
With that tight of a budget I wouldn’t hold your breath.
Something like coreboot is incredibly niche for someone to care about. Newer device like above will be costly because of economies of scale. And for something on a hobbyist level to take off it would need to be at least a few years old + the right person getting the bug up their ass to make it work (well).
I had a W540 until the end of 2021 and besides it crashing from a hardware issue it was plenty fast for me at the time. As long as you’re not doing too intensive work it’s probably plenty as long as you’ve got the full power 45 watt quad core i7s.