GrapheneOS will only run on Pixel devices for now (including the Pixel tablet), see https://grapheneos.org/faq#supported-devices
LineageOS has two Lenovo devices listed, your (and my) tablet are not on that list, see https://wiki.lineageos.org/devices/#lenovo
Depending on the model you might find some custom built ROM on e.g. XDADevelopers, but be careful not to brick your device.
Without support from the vendor they don’t. Mobile computing is so locked down right now that it might be possible that not even the vendor can repair a bricked phone tbh.
Compare it to a broken BIOS on a PC. You can basically throw out your motherboard if you fail while updating it. Some devices have hardware pins used only for provisioning and debugging (JTAG) but they would have to be reverse engineered first.