Bernhard Kau

This plugin will show the first post with its full text but all the others with the text after the “more” tag

First Post Full Length

This plugin will show the first post with its full text but all the others with the text after the "more" tag

Tim Eckel

Try it out on a free dummy site here => <a href="https://demo.tastewp.com/read-more-excerpt-link" rel="nofollow ugc">https://demo.tastewp.com/read-more-excerpt-link</a>
When WordPress makes an excerpt from your post content, it crops the content and adds an ellipsis […] to the end. This plugin changes the ellipsis to a Read More link to the full post content.
You can change the Read More link text to anything you wish from the Read More Excerpt submenu on the WordPress Settings menu.
Also from the Read More Excerpt submenu, you can specify the excerpt word length (WordPress defaults to 55 words).
Additionally, you can force the Read More link to show even when an excerpt is entered or when a read more tag is added to the content. This is turned on from the Read More Excerpt submenu with the Show More Frequently checkbox.
The Read More link uses the class read-more-link, so you can stylize the link any way you wish.

First Post Full Length vs Read More Excerpt Link