They said they were doing that (see release notes).
- Removes the SMART UI (NAS-134927).
- Removes the built-in SMART test scheduling and monitoring interface to improve user flexibility while maintaining smartmontools binaries for continued third-party script compatibility (NAS-135020). Existing scheduled SMART tests are automatically migrated to cron tasks during upgrade, and users can install the Scrutiny app for advanced SMART monitoring.
- SMART tests functions no longer show on the Data Protections Tasks, Storage Dashboard, or individual disk screens.
See Preparing to Upgrade for more information.
The work-around is to trust TrueNAS or use a third-party method such as Multi-Report.