Template Availability -
AEM offers multiple properties to control the templates allowed under Sites. However, combining them can lead to very complex rules that are difficult to track and manage.
Therefore, Adobe recommends that you start simple, by defining:
For an example, see We.Retail: /content/we-retail/jcr:content
The properties allowedPaths, allowedParents, and allowedChildren can also be placed on the templates to define more sophisticated rules. However, when possible, it is much simpler to define further cq:allowedTemplates properties on sub-sections of the site if there is a need to further restrict the allowed templates.
An additional advantage is that the cq:allowedTemplates properties can be updated by an author in the Advanced tab of the Page Properties. The other template properties cannot be updated using the (standard) UI, so would need a developer to maintain the rules and a code deployment for every change.
The following properties determine whether a template T is allowed to be used for a new page to be placed as a child of page P. Each of these properties is a multi-value string holding zero or more Regular Expressions that are used for matching with paths:
Refer fore more details - https://experienceleague.adobe.com/docs/experience-manager-64/developing/platform/templates/templates.html?lang=en