Locale X is a major new version. For all of the new features in Locale X, please see the Locale X release announcement. 10.0.612 is a minor update with the following improvements:
New Material 3 design throughout the app
Improved reliability, especially with bad GPS sensor readings
Note: As a normal part of our release process to ensure high quality, updates to Locale X roll out in phases over a multi-week period. It may take some time before a specific update becomes visible to you.