I turn off my phone every night. Every morning when I turn it back on there's a "Secure Folder Locked" notification that I can't dismiss until I unlock my secure folder.
If it is mainly disturbing for you to see the "secure folder locked" message on the lock screen (unless you've unlocked the secure folder once after reboot) then:
You can disable showing the notification (together with all other android system warnings) on the lock screen. But still keep getting those notifications when you unlock the device.
Therefore: open up the "Android System" notification options, go to notification categories, go to "warnings" or "alerts" category. There select the screen lock notification option "no notifications".
Hence, on the lock screen you will not receive any android warnings (incl. the "secure folder initially locked"). But after unlocking the device all warnings will be accessible.
