This blog post says:
DEP is “always on” for 64bit processes on 64bit versions of Windows and it cannot be disabled.
Also, this Microsoft documentation says this:
On 64-bit versions of Windows, if hardware-enforced DEP is available it is always applied to 64-bit processes and kernel memory spaces and there are no system configuration settings to disable it.
and this:
Per-application DEP configuration
For the purposes of application compatibility when DEP is set to theOptOut
policy level, it is possible to selectively disable DEP for individual 32-bit applications. However, DEP is always enabled for 64-bit applications.