From what I can tell in the project's GitHub repository, there is an outstanding request to add Cassandra 4.0 support (issue #408) but no one from the project has responded to it.
The last supported Cassandra version is 3.11.3 which was released in September 2018 (over 4 years ago).
To me this is an indication that the project is no longer active. In fact, the repository has been archived by the owners on May 2020.
If you want to continue using the plugin, I think you're only recourse is to get in contact with the owner Stratio Big Data. Cheers!
[UPDATE] I've discussed with Andres de la Peña (project contributor, formerly from Stratio) who confirmed that Instaclustr maintains a fork here https://github.com/instaclustr/cassandra-lucene-index and Stefan Miklosovic/Instaclustr confirmed that their fork supports Cassandra 4.0 + 4.1.