it was previously quite easy, but it seems to be getting much harder as Google locks the ecosystem down alongside their push towards manifest v3 (cause nobody can have nice things) and potentially moving their Chromebooks to Android

a used Chromebook might still be a good option for a cheap linux laptop though — your mileage may vary. if you go that route, look for one that lets you replace its bootloader. the Google one is extremely annoying if you’re running a third-party OS, because it’ll wipe your SSD and reinstall ChromeOS if you hit spacebar during boot (probably Google’s way to punish the user for straying too far from the ecosystem)

Most support reflashing the UEFI, but Linux or Windows support is better on some than others. Biggest problem now is disabling write-protect on the flash: used to just be a screw, now you have to use a special USB cable: https://docs.chrultrabook.com/docs/firmware/supported-devices.html#firmware-and-os-support