They ported Windows 10 IoT to run on the pi (it's not a desktop Windows experience though, don't get your hopes up). I'm not sure they maintain or care about it anymore though, I think they moved to Azure IoT that's Linux-based.

There's no porting to be done. You can run Windows 10 / 11 on a Raspberry Pi 400 today.

Windows 11 only up to one of the betas—the production version has some ARMv8.1 extensions that aren't compatible with the Pi's SoC.

The Pi is also woefully underpowered, even when overclocked—the cheaper ARM SoCs from Qualcomm are still 2-4x faster than a Pi 4, and they even feel a bit slow at times running Windows on ARM.

The pi's still a pretty weak machine hardware wise. I imagine full fat Windows would be pretty rough to use which may be why it's not been done.