Thunderbolt 4 is just the combination of Thunderbolt 3 and USB 4. When a user uses a Thunderbolt 3 device, he can connect the Thunderbolt 3 device to either a Thunderbolt 3 port on host, or a Thunderbolt 4 port on host computer for production because Thunderbolt 3 and 4 are just the same – both Thunderbolt 3 and 4’s top performance is 40Gbps. But if a user is using a USB 4 device, then he has to connect the USB 4 device to a Thunderbolt 4 port on host for work. So Thunderbolt 3 and 4 are all the same with the identical 40Gbps transfer speed.

Take Apple’s MacBook Pro (Late 2023) for example: even though it is equipped with Thunderbolt 4 port, on its webpage, it states it still runs with Thunderbolt 3 (40Gbps) signal.
https://www.apple.com/macbook-pro/specs/