Could you please check if we need to update there as well?

looks like we should. But the new command vscode.java.buildWorkspace is contributed via java-debug jdtls plugin and now project manager doesn't have hard dependency on the debugger extension, looks like we should assert if the command is exists at first.

Or can we consider to move the command to jdtls side?

And the logics at the project manager side can be reviewed. E.g., we can only build the given project, instead of the whole workspace, than we can benefit from this change.

JLS supports build specific project: https://github.com/eclipse/eclipse.jdt.ls/blob/d4101ae14289ff7db98763cf731a0c74138589b8/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/handlers/BuildWorkspaceHandler.java#L100

I think we can use that directly for exporting jar task.