Replaced Hard Drive with Compact Flash, Unable to Restore

I’ve wanted to upgrade and restore my Classic iPod 4th Generation for sentimental reasons. I’ve replaced the battery and the motherboard, the final goal was to replace the old 60GB mechanical drive with something less fragile and more power efficient. I’m stuck though, because the Compact Flash card (no matter how I prepare it), can’t be written to once installed in the iPod. I format the Compact Flash card on a Mac as MacOS Extended Journaled, it shows in finder as 64 GB. But if I insert that disk in the iPod and mount the iPod to the same Mac in Disk Mode, it shows as 187.6 GB, with an unformatted partition scheme. If I try and erase the disk in Disk Mode, Finder gives me a generic input/output error.

When I try the same exercise with an ancient 128MB Compact Flash card, it is recognized just fine, but too small to do anything with.

Is there something about this modern day Compact Flash card that is giving me trouble? Stumped.