From your question, I can understand that you are experiencing difficulties integrating the OWL API with MATLAB to load an ontology file and are encountering an error related to MATLAB's inability to recognize the "OWLManager.createOWLOntologyManager" method. I assume that you are using MATLAB R2023b.
This issue is likely because the OWL API JAR files are not on the Java class path in MATLAB. To fix this, you need to make sure that the OWL API JAR files and any other required dependencies are included on the MATLAB Java class path. More details can be found on the documentation page of the OWL API: https://github.com/owlcs/owlapi/wiki/Documentation