The fact that First Aid failed to repair your startup disk in Recovery Mode and gave you the error "One or more volumes are locked" may suggest that your startup disk is encrypted by FileVault. In this case, the encrypted disk should also be grayed out.
To unlock your startup disk or the Container 2 you mentioned, you can select it from the left side and click the Mount button in the toolbar, which should prompt you for a password. After you enter the password, you can run First Aid again to see if it reports errors.
When you rerun First Aid, you can click View > Show All Devices to display all the disks and volumes on your Mac if you haven't already. Then start from the last volume of your internal hard drive until you have repaired the physical disk at the top.
If that doesn't work, consider updating your Mac.
Read Also:
What Is FileVault And How to Encrypt Disk with It
[Solved] First Aid found corruption that needs to be repaired
How to Run Disk Utility First Aid to Repair Disks on Mac
