Hi there,
You can try plugging into another computer or laptop does it recognize it. It may be that it’s bricked but if it’s never been programmed then could be a windows driver issue also. Sketch size is fine btw, I have used many and only ever had one that needed unbricked because I accidently removed the softdevice with nrf desktop programmer app. I used the same to re-write the correct Xiao.img and restored it to a working unit.
HTH
GL 
PJ