Which is preferable using thunderbolt 3 or 4 for time machine backup to new iMac
What is preferable for data transfer to new iMac; Thunderbolt 3 or 4
iMac Line (2012 and Later)
Doesn’t matter if the TM drive is a native TB 3 or 4 device as both support the max transfer of 40 Gbps. The speed difference is only over PCIe where TB 4 is theoretically twice as fast as TB 3.
TB 4 does support longer cables though (I think up to 2m ?).