cgsecurity.org

Hello,

I recently purchased a 4TB WD MyBook and moved about 750gb of files to it for storage. It was formatted as a single exFAT partition. Due to some bad life decisions I accidentally created a new 4TB HFS+ partition, which is still blank, and I need to revert to the old partition. I'm going to try a testdisk deep search overnight as the quick search didn't find the partition, but is that the correct and simplest process for this recovery?

During a HFS+ format operation, a lof of sectors are overwritten with new data. It's probably why testdisk failed to find the old partitions.
You can try to recover your data with PhotoRec but it will not recover the original filenames.