My father was making custom ethernet cables and wondered why he only got 100mbps despite the cable being cat6, after redoing the connectors, 1gbps came up. : r/techsupportgore
Custom Made - Cat6, 23AWG, PE, UTP External Patch Cable, Flush Snagless Cat6 UTP Patch Cables from Paragon Networks
Create your own custom-length ethernet cable | Orbits IT
Pine Tree Audio Octave Audiophile Cat 8 Ethernet Cable CUSTOM LENGTHS USA | eBay