Can't Detect Bootable USB

I’ve never been able to get TransMac to work on my HP system ;-{

I’m not sure if its dependent on the given PC systems USB port services, as I know other have done it and others not!

Lets assume the issue is not TransMac but something with the systems USB ports.

This series has USB 2.1 USB-A ports so USB 3.x connections won’t work (that’s if its strictly a USB 3.x device).

Then there’s the power aspects of the port. Your Mac offers power for low current devices so a full sized 3.5” drive won’t work as it needs more power than what the system can offer.

If the power services have an issue then the only option is to use an external powered USB hub to supplant the MAc’s power services. You could check the systems power using a power meter like this one USB Mini Voltmeter

The last issue is the logic boards USB services has a problem.

So is there a work around?

I think you found it! You just didn’t follow through with the needed commands to enable the proper OS to install! How to reinstall macOS from macOS Recovery heres we want Option - ⌘ - R keys to get the newest OS your system can support. But why? When Apple has a certificate within the installer which expires unless Apple updates it. The older OS’s are no longer signed which is why you got the odd error. Here’s a bit more on this If you've got an old macOS install image, it will probably stop working today

There is a workaround resetting the systems date back in time!

This won’t work in your case as you would need a bootable external drive to run the installer.

OK, let’s try setting up a fresh OS installer manually! You really need to do this on a Mac system.

Go to How to upgrade to macOS Sierra and jump down to Step 4, locate the Blue URL link labeled Download macOS Sierra, download the file and unpack it to get the installer. Now follow this guide: How to create a bootable macOS Sierra installer drive