I’ve only seen 2m T3 cables.
Passive cables longer than 0.5 meters feature only 20 Gbps connectivity so if you want a longer Thunderbolt 3 cable while retaining full 40 Gbps connectivity, you’ll need to spring for an active cable, such as this 2m one from CalDigit or this 2m one from OWC. Active cables contain transceivers in the plugs that regulate data transfer, these transceivers provide the necessary stability over longer lengths, but I haven’t seen any over 2m.