Doom no longer ships ccls as the default LSP, see [here]{https://github.com/doomemacs/doomemacs/issues/2689#issuecomment-2339183572) - I have simply added in the updated instructions from [here](https://github.com/doomemacs/doomemacs/blob/c75e1b915bf7de28ae057aaa7b74221ec943bd74/modules/lang/cc/README.org#lsp-mode-with-ccls)