Tested on OpenBSD 6.3

Prepare ThinkPad X1 Carbon Gen 5 for OpenBSD

Turn ThinkPad on and press F1 to enter Setup.

Select Security > I/O Ports, set Bluetooth and Fingerprint Reader to Disabled. These devices are not supported by OpenBSD. Disable other devices you don’t use.

Select Security > Secure Boot, set Secure Boot to Disabled.

Select Startup > Boot, set Boot Priority Order to:
USB HDD, then NVMe0 ….

Select Startup, set UEFI/Legacy Boot to UEFI Only.

Press F10 to save changes and reboot.

Install OpenBSD.