I noticed that the documentation says that the option for "tu" is for 1 through 7. Unfortunately this is not possible under Windows. There is only the option for 1, 4 and 7. But I would also like to try values such as 6 or 2.
Options list
target-usage (or tu)
Sets the trade-off between quality and speed, from 1 (best quality) to 7 (fastest speed).
Default: 2
You can specify 1 through 7, and HandBrake sets the option accordingly, but most hardware/driver/encoder combinations only support a subset of those and may sanitize/change the value to the closest supported value.
Since the supported target usage values vary depending on the hardware/driver/encoder combination, we cannot indicate which TUs are actually available before you start the encode.
So the technologies are already in Handbrake, but only those technologies that support the iGPU or drivers are used? At the moment I am testing the encode with an I9-9900k - UHD 630. That means that I can use other and better options in Handbrake, for example with a 10900k or later with a 12900k, which I cannot use at the moment?
Target Usage is literally just a number you tell the encoder to use. Whether the Intel encoder actually uses the exact number you tell it to or another one is not up to HandBrake.
IIRC, Target Usage values 2, 3, 5 and 6 are typically only available on older hardware and/or software implementations of Quick Sync Video.