Searching from google brings me to your question in [Unity Forum](https://forum.unity.com/threads/playerloop-run-in-fixedupdate.547864/) and also contains the code for PlayerLoopInterface. Copy pasting it into the submodule resolved the error. However I think you might want to look into that? <img width="363" alt="Screenshot 2021-02-13 at 8 42 20 AM" src="https://user-images.githubusercontent.com/5751850/107836306-9fb88b80-6dd7-11eb-8174-f5635eeef70c.png">