Save site as a template option for publishing sites sharepoint

Save site as a template option is hidden from the publishing sites.
In order to get around this issue you need to update a single property page value in your SPWeb object for the site you are trying to save as a template
and you are good to go. The property is called SaveSiteAsTemplateEnabled. We need to set that property to true that’s all.

Here is the code sample that shows how to do that using PowerShell:

Add-PSSnapin microsoft.sharepoint.powershell -ErrorAction SilentlyContinue
$web = Get-SPWeb http://Web URL
$web.AllProperties["SaveSiteAsTemplateEnabled"] = "true"
$web.Update()


OR

Same can be done using SharePoint Designer.
1)Open web in sharepoint designer.
2)on Ribbon,(right hand last button) select Site Options >> Select Parameter Tab >> Select "SaveSiteAsTemplateEnabled".
3)click on modify button and change value from false to true.
4)click ok.

Well, since the Save site as a template option is hidden from the publishing sites settings page we all used the following URL to go there directly:

/_layouts/savetmpl.aspx

Or

/_layouts/15/savetmpl.aspx