Still facing this issue. The folder structure seems ok to me as the zip file contains the correct Oquonie.pdx folder such as all the other games I sideload to my Playdate from itch.io
I don't have the SDK installed so the Oquonie.pdx appears as an usual folder for me. In the folder I have the pdex.bin pdex.so pdxinfo files and sounds and SystemAssets folders. I'm sideloading thru the playdate website, will try over usb later, maybe that could help