>As of January 2021 deleting SecureBoot keys and installing your own keys (for example by using KeyTool) will brick the device. This is a problem that is similar to one which has been reported on some other Lenovo laptops [0] and is likely due to a faulty firmware. If the device is stuck in a boot loop after replacing the SecureBoot keys, the only way to repair it is by replacing the mainboard of the device.
[0] https://forums.lenovo.com/t5/ThinkPad-X-Series-Laptops/BIOS-...
From https://wiki.archlinux.org/title/Lenovo_ThinkPad_T14/T14s_(I...