The OCaml 4.13 preview for ocaml-lsp-server is now available as well.
To install it along with the OCaml 4.13 rc, please refer to the first post.
If you encounter any problems while using ocaml-lsp-server, please feel free to report it directly in Update to ocaml 4.13 by ulugbekna · Pull Request #506 · ocaml/ocaml-lsp · GitHub