Apple may use a different nomenclature for its M1 successor at tomorrow's Unleashed event. Bloomberg quotes developer sources that claim the names M1 Pro and M1 Max have appeared in their app logs. While it is not clear whether Apple would indeed opt for a delineated nomenclature instead of just using M1X, there is no ruling out the possibility either.
https://www.notebookcheck.net/No-M1X-References-to-M1-Pro-and-M1-Max-show-up-in-app-logs-ahead-of-Apple-Unleashed-event-new-nomenclature-could-offer-better-delineation-of-capabilities.573622.0.html