Does the iMac M1 Thunderbolt3 port support 20 Gb/s for an external storage device with USB 3.2 Gen 2x2?

I am about to choose an external storage to my iMac M1 that comes with four USB ports. Now I see that the external storage Samsung T9 https://www.samsung.com/se/memory-storage/portable-ssd/portable-ssd-t9-1tb-black-mu-pg1t0b-eu/ uses USB 3.2 Gen 2x2 which has the nominal speed 20 Gb/s.

Is that speed supported by the Thunderbolt port on the iMac M1?

According to the technical specifications iMac (24-inch, M1, 2021) - Technical Specifications the Thunderbolt port supports:

• • Thunderbolt 3 (up to 40Gb/s)
  • USB 4 (up to 40Gb/s)
  • USB 3.1 Gen 2 (up to 10Gb/s)

Here it does not mention USB 3.2 Gen 2x2 (up to 20 Gb/s). Does that mean that it is not supported?

But isn't USB 4 backward compatible and then it should support USB 3.2 Gen 2x2 (up to 20 Gb/s), or? But if so, why does Apple then mention USB 3.1 Gen 2 (up to 10Gb/s) explicitly for the Thunderbolt port but not the Gen 2x2?

(In addition, my iMac M1 also comes with two additional ports: "Two USB 3 ports (up to 10Gb/s)", not relevant for the question above.)

The question also seems relevant to other Apple computers such as iMac M3 (iMac - Technical Specifications - Apple) and Mac mini with M2's (Mac mini - Technical Specifications - Apple) which both mention USB 3.1 Gen 2 (up to 10Gb/s) in the tech spec but not the Gen 2x2.