We bought a Lenovo USB-C to HDMI adapter, and get exactly no image on the HDMI port (even after setting thunderbolt up as primary Screen in BIOS)
From Reddit, I can see that it is not an uncommon issue to not et HDMI on USB-C adapters.
Which adapters are tested and confirmed as "working"?
I am using this one: https://www.startech.com/AV/usb-c-video-adapters/usb-c-hdmi-adapter~CDP2HD USB Type-C to HDMI Adapter - 4K | USB-C Video Adapters | StarTech.com on my Lenovo T470 (Work) notebook.
Normally this port is used by the power adapter, but I've kept the old power adapter from the Lenovo T450 so that the USB-C port was free for a second screen (Third if you count the notebook screen).
I suspect there might be some proprietary handshake thing going on with the Lenovo adaptor.
I'll get something else to test tomorrow.
the important thing for us is to use the USB-c/thunderbolt connector as "primary" display, so that it is possible to boot into BIOS using only that display port.