You can also get a refurbished thinkpad with Ryzen and 16gb of ram for 400€ or so on european Ebay.

You seem to know what you're talking about. I used a cheapie Taiwanese Intel netbook for years, on Linux, with great success. When it came to replace it, there was nothing left in that niche (i.e. small and cheap) except ARM Chromebooks with (apparently) locked bootloaders. So I reluctantly bought a heavy and expensive Intel laptop.

Was I wrong to assume that the average big-box-store Chromebook cannot be jailbroken, or has only driverless hardware, or are things changing here? If the latter, surely this opens a boulevard for Linux? Any insight much appreciated.

Buy and support vendors that ship proper Linux laptops. I know of Star labs and Nova Custom in the EU, both use coreboot as well.

I never understood why bother with these.

You get a dealbreaker keyboard because of the lack of an alt key and you don’t even save much money for the effort of working around the Chromebook restrictions. A laptop originally sold with Windows is so much more straightforward to work with.

I’d just grab something like an HP EliteBook 840 G10 on eBay. Around $300, upgradable RAM and SSD, and reasonably recent. Relatively modern/attractive aluminum build.

Or I’m sure there’s some other 2-in-1 not-Chromebook convertible model you can grab if you need the touch screen.