Thunderbolt 4 isn't wildly different from its predecessor, but it does increase the minimum specs. Thunderbolt 3 supported speeds of 40Gbps and dual 4K displays, but what's different here is that it's now a minimum spec for Thunderbolt 4. You might recall that there were a bunch of ultrabooks that used Thunderbolt 3, but with only half of the bandwidth. OEMs won't be able to do that anymore with the new standard.
There are some other improvements though. Thunderbolt 4 now supports cables that are up to two meters, and you can also connect it to an 8K display. Docks can now have up to four Thunderbolt 4 ports, and when a mouse or keyboard is connected to the dock, you can click to wake your PC from sleep.
Intel isn't changing up its Thunderbolt branding. As seen in the image above, there are plenty of ways to recognize the different kinds of USB ports, but only one for Thunderbolt. With Thunderbolt 3, it was easy because it used USB Type-C, while its predecessors had used Mini DisplayPort. Of course, Thunderbolt 4 still uses USB Type-C.
As for when you'll be able to buy a Thunderbolt 4 PC, the answer should be later this year. The new technology will be integrated into Intel's 11th-generation 'Tiger Lake' chips.