Hi there, SATA 3.5 drive being uninitialized is why the "The disk you inserted was not readable by this computer" notification came. In order to make the internal SATA drive readable on your Mac, you should reformat it as a macOS-compatible file system in Disk Utility.
Here is how to reformat the internal SATA 3.5 drive via Disk Utility on your macOS computer:
Step 1: Launch Disk Utility on your Mac.
Step 2: Select the SATA 3.5 drive from the left sidebar in the Disk Utility window.
Step 3: Click the Erase button from the top menu bar of the DU window.
Step 4: Give the disk a name or leave it default.
Step 5: Select a file system in the Format box and APFS is highly recommended.
Step 6: Click the Erase button to begin the reformat process.
Wait for the process to end and then see if the SATA drive is readable on your device.