Blue Snowball ICE microphone not detected by my iMac.

The first generation of these Blue Snowballs had a USB implementation that they mentioned on their support site was not compatible with OS X Mountain Lion or later. Had a friend with one of these and he ultimately returned it, as Blue told him on the phone that it would not work with Mountain Lion. At one time, they had a notice about this on their website, but it has been several years and I have not found that notice since.

I suspect that you will need to go to the Blue Snowball ICE support site to find out, whether or not, they have provided updated drivers for their microphone to work with macOS Mojave. Have you?

I already went to their site. All they have is a manual. They don’t provide any driver files for the MacOS for download for the Snowball series.

Wouldn't know as you didn't provide that information in your original post. All I can assume then is that they expected that their device would work with Apple's genetic drivers. It appears that their "plug and play" microphone, isn't, or, at least, they don't test it with every variation of OS that comes out to claim that marketing statement. Just saying.

I found this on their support site: If your mic fails to work on any computer, please visit our Customer Service request form (requires a Blue Web Store user account). Might be worth a try.