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Sites with the full API available (i.e. with WordPress 4.7+ or the WordPress rest api version 2 installed) will have the wp/v2 item in namespaces as well.
WordPress 4.4 enabled the API infrastructure for all sites, but did not include the core endpoints under wp/v2. without WordPress rest api version 2

https://developer.wordpress.org/rest-api/using-the-rest-api/discovery/

Missing 4.7 here (for /wp/v2/ endpoint, root endpoint is /wp-json) https://developer.wordpress.org/rest-api/extending-the-rest-api/routes-and-endpoints/

Changelog https://developer.wordpress.org/rest-api/changelog/

Guide https://developer.wordpress.org/rest-api/using-the-rest-api/authentication/ ( nonce automatically managed, for WordPress 4.7 or WordPress api rest version 2 plugin ).
JavaScript core https://github.com/WordPress/WordPress/blob/5.3-branch/wp-includes/js/wp-api.js#L840
For developers using the built-in Javascript API, this is handled automatically for you. This is the recommended way to use the API for plugins and themes. Custom data models can extend wp.api.models.Base to ensure this is sent correctly for any custom requests.

I could not locate wp.api.models.Base , but the core file is this.
theoretically javascript must send a header and the is automatically managed.

Good Coding.

Context view GET, request wp/v2/posts?status=publish Does it work as a browser? view requests (GET) do not need authentication for this scenery.

https://wordpress.org/support/topic/theme-403-forbidden/#post-12292401

The DirectoryIndex is the default page served by the server when a user requests an index of a directory by specifying a forward slash (/) at the end of the directory name.

For example, when a user requests the page http://www.example.com/this_directory/, he or she will get either the DirectoryIndex page if it exists, a server-generated directory list if it does not and the Indexes option is specified, or a Permission Denied page if neither is true. The server will try to find one of the files listed in the DirectoryIndex directive and will return the first one it finds. If it does not find any of these files and if Options Indexes is set for that directory, the server will generate and return a list, in HTML format, of the subdirectories and files in the directory. The default value, found in /etc/apache2/mods-available/dir.conf is “index.html index.cgi index.pl index.php index.xhtml index.htm”. Thus, if Apache2 finds a file in a requested directory matching any of these names, the first will be displayed.

https://httpd.apache.org/docs/2.4/sections.html#file-and-web
server config (httpd.conf, htaccess), virtual host https://httpd.apache.org/docs/2.4/mod/core.html#directory

use the private mode of chrome or a browser that has never had access to your website.

XML-RPC functionality is turned on by default since WordPress 3.5.
https://codex.wordpress.org/XML-RPC_Support
some hosting with custom WordPress may use the enable in a different way with the menu or htaccess configurations etc.
even reverse proxies or proxies may block requests to XML-RPC file.

Yes @sterndata is $args = array(); reference https://developer.wordpress.org/reference/classes/walker_category/
From the WordPress repository the latest version of the mystique theme is version 2.5.7 from the manufacturer site 3.3.2 without updates for 8 years. http://digitalnature.eu/themes/mystique/

As of WordPress 5.3 you don’t use the old date and time functions depending on an offset, now use the DATETIME class or functions available from WordPress 5.3.

$container = new DateTime( "Y", new DateTimeZone( "UTC" ) );
$value = $container->format( "Y" );
//or DashBoard settings get_option( 'timezone_string' ) or get_option( 'gmt_offset' )
//Conversion object DateTimeZone https://developer.wordpress.org/reference/functions/wp_timezone/ refer to https://developer.wordpress.org/reference/functions/wp_timezone_string/ 
// php 5.5.0 for offset +01:00

also from wordpress 5.3 it requires exactly YYYY-MM-DD.
The predefined folders for uploading are created automatically by wordpress, it means not applying any code.

if to overwrite the uploads folder you create the code with the DateTime class without Multisite Global Media plugin and you have problems, you can open a ticket bug on https://core.trac.wordrpress.org

• This reply was modified 6 years, 4 months ago by autotutorial.

When you enable multisite and create your network, you cannot set WP_SITEURL or WP_HOME from the Dasboard.
From sites click on edit go to settings and look at the two urls