In v5.9.0 (released August 2022), Ghost added native comments.

Native comments are supported in v1.3.0 of Range but if your site is running a previous version, you can add native Ghost comments very easily.

Open post.hbs and go to line 97. You'll see code for Cove comments already in the theme:

{{#if @custom.cove_id}}
<div class="post-content pb2">
{{> comments}}

To add native comments, you can remove the code above and replace it with the following:

{{#if @site.comments_enabled}}
{{#if comments}}
<div class="post-content pb2 pt2">

This will enable Ghost comments on every post, which looks like this: