meta-description for "tag" and "categories" pages - metadata

Question

For HEXO blog... I know that meta-description is written in config file and works across all pages.
For blogposts I can create individual meta-descriptions and that works for the search engines.
However, my "tag" and "categories" pages get indexed now and with meta-description of home-page.
This is not good.
So I am asking if it is possible to create a custom meta-description for "tag" and "categories" pages?
Something like...
description: this is a page about {{tag}}
and
description: this is a page about {{category}}
This is the code in my head.ejs.
The site main config file has description: main config meta-description text.
<%if(metaDescription){%>
<meta name="description" content="<%= config.description %>">
<% } else if (page.description){ %>
<meta name="description" content="<%= page.description %>">
<% } else if (page.excerpt){ %>
<meta name="description" content="<%= strip_html(page.excerpt).replace(/^\s*/, '').replace(/\s*$/, '').replace(/[\n,\r]/g,'') %>">
<% } else if (page.content){ %>
<meta name="description" content="<%= strip_html(page.content).replace(/^\s*/, '').replace(/\s*$/, '').substring(0, 150).replace(/[\n,\r]/g,'') %>">
<% } else if (config.description){ %>
<meta name="description" content="<%= config.description %>">
<% }
<% if (page.keywords){ %>
<meta name="keywords" content="<%= page.keywords %>">
<% } else if (page.tags){ %>
<%
var thistags=[];
page.tags.each(function(k){
thistags.push(k.name);
}) %>
<meta name="keywords" content="<%= thistags %>">
<% } %>

Answer 1

This is all handled by your theme so you need to add the logic there.
You need to check if your page is a tag or category index and generate a custom description there:
let description = page.description; // Normal case when your desc comes from meta data
else if (page.tag) {
description = 'This is a page about ' + page.tag;
} else if (page.category) {
description = 'This is a page about ' + page.category;
}
// Use your description variable as you are currently doing
EDIT: based on post update (added head.ejs)
else if (page.tag) {
<meta name="description" content="<%= 'This is a page about ' + page.tag %>">
} else if (page.category) {
<meta name="description" content="<%= 'This is a page about ' + page.category %>">
}