how to manage excerpt and full content of posts

Hello,

I created a page that only displays some posts according to their category, by creating a new template for this page. I would like that this page shows the full content of the posts. But I also would like that the page displaying all the posts shows only excerpts.

If I replace ? the content ? by ? the excerpt ? in the content.php file of my child theme, every post displays only the excerpt, even the single post. So I added ” is_singular() ? the_content() : the_excerpt(); ? and it worked for the single post but I don’t know how to apply a similar rule to my new page template…

Is it possible ? And in this case how to create a read more button for the excerpts?

Thanks in advance for your help