With the "Migrating to MDC-based Angular Material Components" most/all angular material components where refactored to follow the new concept but the components in the old version are still available as "MatLegacyXXX". However I did not find any information, when these components will be removed.
Are they still available in angular 16?
TL;DR The legacy components are available in v16, but not anymore since v17.
Angular Material is developed by the Angular team and follows common Angular practices. From Angular's deprecation practices:
When an API or a feature is deprecated, it is still present in the next two major releases. After that, deprecated APIs and features are candidates for removal.
This means that legacy components are still available in both v15 and v16. According to the Angular 17 blog post, the legacy components were removed with v17. However you should be able to use @angular/material v16 with the legacy components in an Angular v17 app.