Mouse cursor trail settings cannot be saved; they are disabled after a restart.

Since “Show pointer trails” saves until sign-out or restart, the setting is probably being overwritten at logon rather than failing to apply. Start with the new-account test: create a temporary local account, enable trails there, then sign out and back in. If it persists, the original user profile is affected; migrate to a new profile instead of repeatedly changing the registry. If it resets in both accounts, perform a clean boot: in System Configuration hide Microsoft services and disable the remaining services, then disable startup apps in Task Manager. Restart, enable trails, and test again. If it now persists, re-enable items in groups until the cause is identified. Also check whether the PC is work-managed, because policy can reapply settings at sign-in. Finally, update Windows and reinstall the mouse driver in Device Manager. If clean boot changes nothing, run DISM RestoreHealth followed by SFC /scannow, then retest.