Do not format the drive. Do not run CHKDSK. These will worsen your chances.
Recovery of 13fe 50x USB devices is a two-path problem: either accept data loss and reflash firmware for device reuse, or perform invasive NAND reading with FTL reconstruction. Given the proprietary nature of Phison’s mapping, future research should focus on reverse engineering the scrambler for open-source implementation. 13fe usb disk 50x usb device recovery