I am running Windows 11 on my test laptop with Intel Core 2 Duo dual core unsupported system (see my 1st system specs) and on my main PC with 3rd generation Intel Core i7 3770 unsupported system (see my 2nd system specs). Both installations are on Legacy BIOS mode (MBR) without TPM 2.0 without Secure Boot. My laptop doesn't even have WDDM 2.0 graphics drivers, only WDDM 1.x, so is the most unsupported. Both computers run the official 21H2 release (not Insiders or Dev) and updated to the latest available update, I have even installed the new optional update up to 22000.778 Never was any warning about compatibility. I never had to hack anything to install Windows updates. I used a hybrid Windows 10/11 USB Flash drive to bypass compatibility check for the initial installation only. Never had to hack again. I just search with Windows Update and install anything it finds (except optional drivers of course, so as not to break anything). If you wonder what is the oldest possible system you can install Windows 11 on, I have already said on an earlier post that it is an old Intel Pentium 4 6xx socket 775 64-bit (yes, that is one of the first Intel 64-bit CPUs) with 2GB RAM and IDE hard disk (not even SATA). As long as you can find at least Vista 64-bit drivers for the graphics (that is at least WDDM 1.0) and you have an Intel 64-bit or AMD 64-bit CPU, you can install Windows 11 on. The exception are the first generation AMD 64 CPUs that lack the necessary instructions to install Windows 8.0 64-bit or higher. These either take up to Windows 7 64-bit or Windows 10 32-bit.
PS: If there is no WDDM 1.0 or higher graphics driver, then Windows use Microsoft Basic Display Adapter which has no hardware acceleration (all visual effects are done in software) so the CPU usage is always high and the system is slower than with a WDDM graphics card. To improve performance just disable all useless visual effects such as transparency and fades.