[plain OM]

any ideas with your 2007 ?

It does sound as if the immobilizer is kicking in, but that's sort of rare IF the car and keys had been working up to that point.

There was a similar case here not to long ago in a later generation Outback (with short video showing the stall) but would have to find thread . . .

 

[plain OM]

Also, the car died during driving and then started exhibiting this startup behavior (automatic transmission, btw)

So this problem actually started (no pun) while driving, i.e., the car died while driving, and not when first trying to start it after it was stopped for a while.

I see that the fuel pressure was checked; what was the result, and did it hold up for the short time the engine will run?

The only thing is that I replaced the air filter 2 days ago. It ran fine yesterday but, then this started today.

Check that the connection to the MAF/AIT sensor, and the sensor itself, hasn't been disturbed. It's not unusual when trying to get to the air filter.

 

[plain OM]

I cannot believe that this condition would cause a shutdown while driving

The air filter will normally stop it, however, when the filter is being removed, larger objects on the filter can fall off the vertical filter and drop down into the case on the downstream side. After the new filter is installed, and the engine is started, it's sucked up into the air flow, some of which goes through the MAF sensor.