External Hard Drive not detected on File Explorer & Disk Management

With these Shingled Magnetic Recording disks, hours of writing will fill the CMR cache. Once the CMR cache is filled, the HDD becomes extremely busy clearing the CMR cache by moving the contents onto the clobbered slow SMR. During that, it is common for HDDs to disappear temporarily. This doesn't mean your HDD is any more defective than it was new, but all SMR disks are defective to some extent. If your Seagate HDD is from 2019 or later, the reliability should be good, as the new CEO has greatly improved quality over the past 4 years.

The reason why SMR is used is because the technology for reading allows narrower tracks, but the technology for writing currently does not allow tracks to be written as narrow. The workaround is to overlap around half of each track with the next, but that requires multiple tracks to be rewritten and results in write amplification. 500 GB is plenty small enough to use Conventional Magnetic Recording, so this disk only uses SMR because it's cheaper than having another platter.

To test a disk, download openSeaChest and open Command Prompt as administrator. Type cd C:\Users\[username]\Downloads\openSeaChest_Windows_x64 and press enter. Input OpenSeaChest_SMART --longDST --poll -d PD# replacing # with the disk number of the Seagate external HDD as shown by Task Manager.