Have you connected the encrypted drive to the old Mac and check whether it is working there? If you can still use the drive on the old Mac, try to decrypt the drive on the old machine and connect it to your new MacBook Pro again.
Generally, the encrypted external hard drive on one Mac should be accessible on another Mac with the correct password. As you said there is no partition and volume, it seems that the external hard drive is corrupted. Then, if there is no backup, you can rely on third-party data recovery such as iBoysoft Data Recovery for Mac to recover data.
After recovering data from the corrupted drive, you can then fix a corrupted external hard drive on Mac:
1. Run Disk Utility First Aid again.
2. Use the FSCK command in Single User Mode.
3. Reformat the external hard drive on Mac.