Hey, simply speaking, either the system bugs or the external hard drive issues make your Mac can't recognize and read files on your external hard drive.
You can follow my tricks below to fix your external hard drive not showing up on Mac and read files on it:
1. Check your connections. Are you sure your external drive is connected tightly and correctly to your Mac? You can unplug the drive and reconnect it to another port, or change a USB cable until you find it shows up in Disk Utility. If the external hard drive still doesn't show up in Mac Disk Utility, the drive may have hardware issues, contact a repair center.
2. Run iBoysoft DiskGeeker to check the status of the external drive.
- Free download, install, and launch iBoysoft DiskGeeker.
- Select the drive on the left sidebar and click "First Aid" on the right toolbar to check the external drive and repair the found errors on it
3. Manually mount the external drive. If you can't read files on the external drive as it shows "Not Mounted" in iBoysoft DiskGeeker, click the Mount button on the right-side toolbar to manually mount it. Then, your Mac and Adobe Bridge will recognize files on the external drive.