2015 Lexus RX 400h. Yesterday, driving in rain with wipers set on "Auto" rain-sensor mode, both wipers rotating fine, then suddenly the passenger side wiper retracts into its bottom position and stays there, while the driver-side wiper continues to work fine.
Pulled over and idled, switched the wiper stalk position from Off through Auto, Slow and Fast - no position started up the passenger side wiper again.

Is this a DIY fix (single fuse, minor part installation,) or does this require dealer/mechanic?

 

It appears that one of the wiper linkage arms has become disconnected or some linkage connection point has stripped teeth. You may be able to see something just opening the hood.

I recommend you have an independent car repair shop to inspect your windshield wiper linkage for damage. I would not go to the dealer as they usually overcharge and underperform on older vehicle repairs. This should not be that difficult to fix. Use Yelp and Google for reviews of local car repair shops, or ask friends & relatives.