Firevault Encrypted Disk (now external)

The reason you cannot read anything in those folders is because you are using a different User ID for each Mac for your user accounts (permissions are base on UserID and not usernames). You can drag & drop those locked folders which will have macOS prompt you for an admin password which will then copy the entire folder.

Another option is to use Carbon Copy Cloner (CCC) which will also prompt you for an admin password plus CCC allows you to select exactly which items you want to transfer.

Hello atherrizvi,

Welcome to Apple Support Communities. We understand that you're unable to access your data with FileVault been turned on your old Mac, and we'd be happy to look into this with you.

In this specific situation, you'll need to mount the drive on your Mac then use Disk Utility to turn off encryption. Select: File menu > Turn Off Encryption. You will be prompted for a password again.

Please check out these helpful links:

Use FileVault to encrypt the startup disk on your Mac

Turn off FileVault encryption on Mac

How does FileVault encryption work on a Mac?

Change permissions for files, folders, or disks on Mac

How to remove Filevault encryption within Recovery Mode in Catalina?

Under: "Apple recommended"

We hope this information is useful. Kind regards.