Since your USB key was not old, there are only 2 remaining causes to this USB key
you cannot open through `Disk Utility` or through command line:

- The USB female connector is dirty, to check this best case, just use a compressed air can to clean it. Next test again to open your USB.

- Your USB was key damaged through an electric discharge. This could happen when an external device is disconnected when a write¹ operation is in progress. Due to the rapid voltage change on the connected USB key, an induced voltage peak will occur which could damage the internal electronic of the USB key. The damage will depend on how well the USB key was conceived to sustain such an electric over surge. This could also happen when you touch the conductive male USB connector when you have accumulated a lot of static electriciy ( for example upon removing a sweater made of synthetic fabric, the instantaneous electric voltage can reach 10000 V ). See also [damage to electrical appliances by unplugging them][1]. In this worst case, nothing will fix your USB. It is electronically dead. You will never be able to see the physical damage ( it requires breaking it and a microscope ), but just after the event you undoubtly smell it: specific smell of the produced ozone.
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¹ Why write? Because inside moderne storage write requires more voltage to erase information.

  [1]: https://diy.stackexchange.com/q/160238