P, Pioline (Cognizant) Thanks for posting your question in Microsoft Q&A. Yes $reindex
operation is supported in open source FHIR and check out a sample PR: Add support for Reindex request against a single resource in this regard (Check out related source code path).
Note: Currently, not all search parameters are supported (unsupported-search-parameters.json list), and you may have to refer this discussion for a workaround if incase it is not supported.
For any other questions or feedback specific to microsoft/fhir-server repo, feel free to submit via Issues or Discussions page. Our product team will help you with the answers. I hope this helps and let me know if I can help with any other questions.