Dear @serpro69: I think you did not understand my post at all, so please allow me explain once more.
Ubuntu (and other open-source Linux distributions) are fully modular and therefore can be made fully compatible with Alder Lake (or other hardware like Arc GPU) by Intel, OEM (like Dell), software company (like Canonical) or even the end user. Windows 10 is a closed-source product so it can be made compatible with Alder Lake by Microsoft and Microsoft only.
You made the argument that the lack of Windows 10 could not be only a compatibly matter because Ubuntu 20.04 was available for new Precision 5x70 systems, and there you were wrong. Ubuntu 20.04 can be and will be (thanks to customs kernels) fully compatible with Alder Lake. Windows 10 will not.
Dell is providing customs kernels for Ubuntu, and also mainstream kernel 5.18 will be available this summer for Ubuntu 20.04.5 (and of course 22.04.1).
Edit: Maybe you did not know that, but Ubuntu LTS is semi-rolling release distribution [i.e. it gets not only security updates but also prompt upgrades for crucial packages including the kernel]. For example, the original Ubuntu 20.04 LTS was released in April 2020 with the kernel 5.4, so of course it has not support for Alder Lake at all, but we are currently on Ubuntu 20.04.4 with support for Alder Lake, and in the summer there will be Ubuntu 20.04.5 (and the new 22.04.1) with kernel 5.18+ and full support for all Alder Lake features (like the Thread Director).