You can’t connect two hybrid fibre HDMI cables together without a powered device between them. At the source end, one end of the cable acts as an HDMI sink, receives the signal from the source, converts it into light pulses, and sends them along the fibre; at the other end you have a second device that functions as an HDMI source - it receives the light pulses, and converts them into an HDMI signal that drives the display. But each of the two devices at the ends of the cable draws power from the HDMI socket it’s connected to; unless you have a powered device at both ends of the cable, it won’t work.
(If you’re wondering why “hybrid” fibre, it’s because there’s still a simple electrical wire connection along the cable from the display to the source which carries the EDID signal).