There are some Intel processors which have only IA32 support but can run Windows 10. Pentium 4 Pentium M Core brand before Core 2 (Yonah microarchitecture) I don't know if there is someone still using Windows 10 Build 1904x on these devices. Also, I want to know f there is someone still using Windows 10 Build 1904x on devices which only have 32-Bit UEFI support and have no CSM support. I ask this question because I'm considering saying goodbye to 32-Bit x86 support for projects maintained by myself. (Of course, I only remove 32-Bit x86 support for binaries which minimum system requirement is Windows 10 Build 1904x if I decided to do that. So, the parts which need to support before Windows 10 Build 1904x won't be affected by that.) Kenji Mouri
You, like many other people, are not figuring the matter correctly. 32bit support is important not because the old HW, it's important because a 32bit VM takes 1.6 less storage, 1.6 less RAM and so on. Which means HUGE saving on virtualized environments, when you may have a single server running 20+ VMs In short, a server that can run 20 AMD64 machines, can run 30 or more 32bit machines on the same HW. Long live 32Bit!!
Even old P4 processors support SSE2 and are not IA32 (which refers to a CPU not supporting SSE even, only MMX at best). SSE3 exists since Prescott P4. The Windows 8 and 10 problem was rather with the NX bit (No eXecute) hardware support (or the lack thereof).