USB4 will be backwards compatible with USB4 Version 1.0, USB 3.2, USB 2.0, and Thunderbolt 3. It will also align with the latest versions of DisplayPort and PCIe.
Most home users might be perplexed as to why they've never heard of USB 4, the standard that USB 4.0 version 2.0 seeks to replace. The widely used USB 3.2 standard was intended to be doubled in performance by the August 2019 announcement of USB 4. The minimum throughput requirement for USB 4 devices is 20 Gbit/s, which is the same as the maximum throughput that USB 3.2 offers, even though the standard does permit up to 40 Gbit/s.
Although there are USB 4 cables and goods like docking stations and external hard drives available, most items still use USB 3.2 or even older standards.
It will be up to phone, laptop, PC and USB cable manufacturers to implement the technology. It's another win for USB-C, which Europe has decided to standardize on for all phones and gadgets.