Try this:
- Press the reset button on your MKR WAN 1300 twice quickly. You should now see the built-in LED continuously pulsing to indicate that the bootloader is running.
- Select the port of the MKR WAN 1300 from the Tools > Port menu. It will probably have a different port when the bootloader is running so don't assume you already had the correct port selected.
- Attempt an upload.
If things work out well, this will allow a successful upload. The hope is that after a successful upload using the "double-tap" technique, you will be able to upload normally. Please let me know what the results are.