By 2020 Outback started
By 2020 Outback started having overnight battery drain problems after 21 months, 8K miles. I too suspected that I would be told that I wasn't driving the car enough (COVID collateral damage). However, when I took the car in to be serviced, they discovered that the dome light in my cargo area was in the "ON" position (they discovered this via testing the fuse draws when the car wasn't running). Sure enough, when the dome light was changed to the "DOOR" position, the problem went away.
The above problem was occurring for 5-6 weeks. The constant draining and recharging of the battery eventually killed the battery. Unfortunately, the battery took its last gasp of breathe when I was 30 miles from home. I couldn't jump start the battery so I had to replace it by walking to an auto parts dealer and buying a new battery. To make matters worse, when I took the car in for service, the dealership would not honor the new car battery warranty because the failed battery was not installed in the engine compartment (I had the failed battery on the floorboard of the rear seat). I did convince them to test the failed battery which confirmed it was totally dead. This nonsense of not honoring the battery warranty because it was not in the engine compartment is a total joke. What was I supposed to do, switch batteries after I drove into the service department? I've written a letter to Subaru corporate about this. It will be interesting to see what they say (or not).
Last comment: the dome light in the cargo area being in the "ON" position was totally accidental. I didn't even realize it existed and there is certainly no dashboard indicator that its enabled. I've since put a piece of tape over the dome light on/off/door switch to prevent this from accidentally happening again. This most likely happened when I was putting larger objects into my cargo area :(