Is this the Plugin you are talking about?
If so, yes, that plugin was last updated 4 years ago!!!!!
See this warning at the top of that plugin’s page:
This plugin hasn’t been tested with the latest 3 major releases of WordPress. It may no longer be maintained or supported and may have compatibility issues when used with more recent versions of WordPress.
Consider finding a different plugin that is up to date.
- This reply was modified 5 days, 4 hours ago by t-p.
I am the developer of that plugin and the plugin works fine for WordPress 5.5.3 so I just updated the readme.txt file and uploaded to the plugin repository (http://plugins.svn.wordpress.org/wp-labur/trunk/readme.txt) what I want to do is to hide that warning.
The version tested up to is taken from the stable version’s files, in your case 1.0.1.
Adding a readme and udating the tested up to header in https://plugins.trac.wordpress.org/browser/wp-labur/tags/1.0.1 will fix this issue for you.
You need to have a readme.txt in the actual stable version. You don’t have one here:
Make a readme for the stable version.
Thank you. Following Otto’s steps I solved my issue.