Users are not allowed to access Windows' source code. And according to
Section 2c of
https://www.microsoft.com/en-us/Useterms/Retail/Windows/10/Useterms_Retail_Windows_10_English.htm
:
Restrictions. The device manufacturer or installer and Microsoft reserve all
rights (such as rights under intellectual property laws) not expressly
granted in this agreement. For example, this license does not give you any
right to, and you may not:
(i) use or virtualize features of the software separately;
(ii) publish, copy (other than the permitted backup copy), rent, lease, or
lend the software;
(iii) transfer the software (except as permitted by this agreement);
(iv) work around any technical restrictions or limitations in the software;
(v) use the software as server software, for commercial hosting, make the
software available for simultaneous use by multiple users over a network,
install the software on a server and allow users to access it remotely, or
install the software on a device for use only by remote users;
(vi) reverse engineer, decompile, or disassemble the software, or attempt to
do so, except and only to the extent that the foregoing restriction is (a)
permitted by applicable law; (b) permitted by licensing terms governing the
use of open-source components that may be included with the software; or (c)
required to debug changes to any libraries licensed under the GNU Lesser
General Public License which are included with and linked to by the software;
and
(vii) when using Internet-based features you may not use those features in
any way that could interfere with anyone else’s use of them, or to try to
gain access to or use any service, data, account, or network, in an
unauthorized manner.
And many other sections in the EULA prevent what free software allows, by
definition.
