I believe the issue you are facing is due to your SD card size.
“Large Storage Capacity: With a 64GB microSD card included and support for up to 128GB of expandable storage, the Miyoo Mini Plus+ offers ample space to store a vast collection of retro games, giving it an edge over other handheld consoles with limited storage options.”
Per Droix, link below
https://droix.net/product/miyoo-mini-plus/#:~:text=Large%20Storage%20Capacity%3A%20With%20a,consoles%20with%20limited%20storage%20options.