There was a discussion some time ago about alternatives to Languagetool
There is news.
The current edition of Linux Magazine ( April 2025) contains an article on an extension called Linguist
It reports statistics on a document and derives a readability score.
It is not realtime like Languagetool. you process the document as a whole.
It is suggested the Linguist is currently rather new , but may evolve into a complete Languagetool replacement.
Worth a look?