There's something else going on: uploading is not proceeding correctly. I loaded a trivial (1488 byte)s sketch. It verified. But 'Uploading' remained for a minute or two, and then the error report appeared, dominated by
avrdude: stk500_recv(): programmer is not responding
Same with Blink and other sketches.
Re-starting IDE didn't help. No clues in Device Manager.
Next steps probably:
- change port
- try different cable
- try IDE 2
- reboot Win10 PC.