Currently trying YunoHost now, though for some reason it says my GMKtec G9 has a MMC/Micro SD?

That’s because it probably does. The 64GB of “eMMC” storage that comes on the G9 (I went and looked at their product page) is the exact same type of storage that SD cards use. eMMC storage devices pop up in Linux as /dev/mmcblkX (generally X = 0 for single eMMC storage devices), with their partitions tagged on the end of that device as p1, p2, etc.