backup of boot disk not recognized on any other OS

Hello,

as a precaution I backed up my entire boot disk with Carbon Copy Cloner to an external drive when I recently successfully upgraded to Catalina. This meant my previous backup was redundant (I have other backup methods in place too) and I wanted to use the external drive where the old clone was for normal use for data.

But this does not seem to be possible since macOS and Windows don't recognize the drive. For example in macOS it doesn't show in the Disk Utility and diskutil list also doesn't list the device.

When I have it plugged in while booting, Clover shows the install in the boot screen and I can use this backup install from the drive as usual. Only in this install the external drive is recognized and listed by name, every other OS or computer does not recognize it.

Is this normal and what can I do to reformat the drive to be able to use it like a normal drive again?

Since I don't think it's related to my config, I haven't posted it here. If you think it might be, I will be happy to do so. If relevant, the disk is a WD Elements Portable.

Thanks!