For those interested, Wikipedia says there's no native/builtin 64bit NTVDM due to
> In an x86-64 CPU, virtual 8086 mode is available as a sub-mode only in its legacy mode (for running 16- and 32-bit operating systems), not in the native 64-bit long mode.
...
> The NTVDM is not supported on x86-64 editions of Windows,[31] including DOS programs,[32] because NTVDM uses VM86 CPU mode instead of the Local Descriptor Table in order to enable 16‑bits segment required for addressing[33] and AArch64 because Microsoft did not release a full emulator for this incompatible instruction set like it did on previous incompatible architecture.
Personally, since Microsoft still releases 32bit builds of Windows 10, I just dual boot 32bit (~48GB)/64bit (~900GB) partitions and run the 16bit programs natively on an old Thinkpad.
[0]: http://www.columbia.edu/~em36/ntvdmx64.html
[1]: https://github.com/leecher1337/ntvdmx64
[2]: http://www.columbia.edu/~em36/otvdm.html
[3]: https://github.com/otya128/winevdm
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For those interested, Wikipedia says there's no native/builtin 64bit NTVDM due to
> In an x86-64 CPU, virtual 8086 mode is available as a sub-mode only in its legacy mode (for running 16- and 32-bit operating systems), not in the native 64-bit long mode.
...
> The NTVDM is not supported on x86-64 editions of Windows,[31] including DOS programs,[32] because NTVDM uses VM86 CPU mode instead of the Local Descriptor Table in order to enable 16‑bits segment required for addressing[33] and AArch64 because Microsoft did not release a full emulator for this incompatible instruction set like it did on previous incompatible architecture.
https://en.wikipedia.org/wiki/Virtual_DOS_machine#Windows_NT...
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Personally, since Microsoft still releases 32bit builds of Windows 10, I just dual boot 32bit (~48GB)/64bit (~900GB) partitions and run the 16bit programs natively on an old Thinkpad.