Currently there is no Springer Nature-wide policy on code sharing. However, many Springer Nature journals have policies applicable to software and code. As examples, here are the BMC software policy and the Nature Portfolio software policy.
Please check the Instructions for Authors or Submission Guidelines of your chosen journal for specific policies relating to code sharing. Where a journal does not have specific policy relating to code sharing, you may take inspiration from the sharing practices of your research community, or follow the equivalent data sharing policy, though neither of these are required. For more information, please email firstname.lastname@example.org.