Even when you connect two TB4 equipped Macs, you still have to tell at least one of them to do something before they are really connected with anything Thunderbolt. I am talking about target disk mode which turns the Mac into a dumb drive, or Thunderbolt bridge networking.
To my knowledge the iPadOS can do neither of these, so connecting it to a Macs will fallback to a USB3.1 (10Gbps) instead. I myself have been backing up my M1 12.9" to Macs since the beginning, always used a TB4 cable, the speed is more than fine, especially when compared to Lightning (USB2.0 480Mbps...). I imagine for most usage the 10Gbps is fine.
Then I think a TB4 speed out of the iPadPro starts to be meaningfully useful when transferring video file frequently, which should happen quite often for people who uses FCPX on iPad, or shoot with the iPad camera and wants to transfer the files back on a Mac.