Earlier quoted context omitted.
Can you use the kernel from win11 with win10 (or even 7) userspace, or are NT kernels not interchangeable like this?
I'm surprised you're asking this because it's quite optimistic. No, it's not possible. The best you can do is probably patching Win11 to somehow use Win10-ish UI features.
The somewhat-underground far-East communities have made weird chimeras of different Windows versions. I've seen Windows XP explorer.exe running on a Windows 7 kernel. No idea how stable or usable that is, but it's been done before.