tested with thinkpad x1 carbon gen 5 and openbsd 7.7
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.