If I'm not mistaken, several properties of the client capabilities of diagnostic pull requests are missing:

• relatedInformation
• tagSupport
• codeDescriptionSupport
• dataSupport

LSP4J currently only defines property relatedDocumentSupport.

I'd provide a pull request if you can confirm that these properties are indeed missing.

How it's defined in LSP4J: https://github.com/eclipse-lsp4j/lsp4j/blob/main/org.eclipse.lsp4j/src/main/java/org/eclipse/lsp4j/Protocol.xtend#L9937

LSP spec:
https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#diagnosticClientCapabilities