There is no officially supported way to understand Xcode projects outside of Xcode, for example there is nothing like libSwiftPM which the SwiftPM team commits to support as a way of understanding SwiftPM projects. Unless this situation changes, we do not intend to support Xcode projects outside of the Xcode IDE. Xcode itself will change to provide its settings directly to sourcekit-lsp, when used from inside the IDE.
People have devised methods for getting a compilation database out of an Xcode project, you may want to look into these, the compilation database is something we intend to maintain first-class support for.