Hi there, facing the USB drive not showing in the Disk Utility issue, there are 10 solutions that you can have a try. The easiest ways are manually showing external hard drive in Disk Utility on your Mac or rebooting your Mac computer to fix this issue. But if they fail to make your drive visible in Disk Utility, there are 8 more solutions for your reference.
1. Check the external hard drive in System Information.
2. Reset the USB ports of your Mac.
3. Check for hardware and software updates.
4. Run a virus cleaner software.
5. Run Mac diagnostics to detect hardware issues.
6. Reset your Mac's NVRAM or PRAM.
7. Reset the SMC on your Mac.
8. Ask for help from local technicians or data recovery service.
The article in our website tells you all details about every solution and you can visit it to deal with your trouble: How to Fix External Hard Drive not Showing up in Disk Utility?