<q-args> does not escape backslashes when used with some commands on Windows

[Bakudankun]

Steps to reproduce

1. vim --clean
2. :sourse next script

command! -nargs=? MyCd cd `=<q-args> ?? $HOME`
MyCd Desktop\

3. Vim raises:

E114: Missing quote: "Desktop\" ?? $HOME
E480: No match: `="Desktop\" ?? $HOME`

This seems to be Windows-specific.

Expected behaviour

<q-args> is expanded into "Desktop\\" and :cd Destop\ is executed.
E344 should be raised if Desktop directory does not exist.

Operating system

Windows 10 Pro 21H2

Version of Vim

8.2.3750

Logs and stack traces

No response