The rear gate on 2004 Subaru Outback will not open with key or electric locks. How do I open the gate?.

no year car told. the now lost free users guide is by year.
made 1994 to present (even 1989 as legacy outback)
no country told at all
sorry cars not the same world wide.

open glove box, read the users guide? oops locked too>?
most cars sold in USA , called wagons
opening the rear gate hatch by accident driving
kids fall the ground, or cargo hits cars behind you. (so is illegall that feature)
and is never called a truck ever, in a wagon
only on sedans. a hatch or 5th door it is named.
In Europe then even call them 5 door cars.
so I am confused.
so all keys lost to the car. and can not drive it
nor open any side doors
and rear hatch is locked and valuables in cargo area to fetch, right?
I say call a locksmith
and pick the lock.
the door lock(mechanism) in the hatch internal, is accessed from the inside of the hatch open.so no why to attack it that way.

call a locksmith,

Proceed to a complet reset of all electronic
« Turn the key to ON but don't start
remove batterie cable until all light shut off.
remove your key complety.
plug batterie »

Now you can try your rear gate.

I'd bet that one of the electrical connections is not back on fully. A video below (First few seconds) shows how to look a this. minimal tools needed. How To Install Replace Master Power Window Switch Subaru Outback 00 04...

Subaru Keyless Entry Security Alarm Immobilizer Key Remote Start Systems...

This is moisture in the lock or associated hardware. Heat the key or use a de-icer in the lock.

Is it a lift back or window and tail gate? Either way, there is a little hole on the inside for the escape hatch. Take a small pin, wire, coat hanger, push it straight in, it should pop the window, door, whichever, might be a small button over the hole, that way you can get the door lock fixed without smashing the lock off. I never tried mine , but I know all cars have them now. Check it out.

How To Install Replace Change Taillight and Bulb 2000-04 Subaru Outback

Unfortunately, you will have to remove the panel of the door, Use flathead screwdriver to pry open. It is very likely the spring fell off.

Get a lock cylinder from a dealer and have it re-keyed to your key!

if you get it open spray the latch with PB blaster. do the same with other doors