Type C port in Librem 15v3 is 3.0 port. You can’t connect display with usual USB3.1 to HDMI adapter. Alternatively, you can buy special USB3.0 to HDMI adapter. It need special drivers and may not work properly.
Also you can try to find USB3.1 extention for M.2 port, if it exist. But i definely know that M.2 to PCI-E adapters exist, and PCI-E to USB3.1 adapters exist too.