Hello, it appears that this project's support for Groovy is based on the 3.x line, scoped to org.codehaus.groovy namespace. Groovy 4 has been released under new coordinates from the ASF. It would be great for thymeleaf-layout-dialect to start supporting Groovy 4 as well. I don't anticipate this to be a lot of work, and hopefully should remain mainly cosmetic, changing package names and references like that.

If you'd like and are open to it, I am happy to submit a pull request and accommodate this change. Thank you!