Start the Subaru Impretz AWD 1997 2000GT after a flat battery

Was the battery fully recharged or just partially? What was done or happened besides the battery going flat?

Check compression. Check fuel pressure. What kind of spark is it getting? Can you hear it as well as see it? Is it bright blue or white?

Do you live anywhere near a store like Autozone, Advanced, O'Reilly's, or Pep Boys? They rent cheaply and loan for free.

You said the fuel pressure "is there". What does that mean? 26-31 PSI? Or that fuel is seen coming out of a line?

Well, that sucks. It makes diagnosis a wee bit more difficult.
You said the car sat for over a month; just because it ran great prior to sitting, doesn't preclude a problem developing in the interim.
Not being able t check compression makes it difficult also, because varnish buildup while sitting could have caused one or more of the piston rings to stick to the cylinder wall. When you cranked it over, these rings could have cracked or snapped, causing a loss of cylinder compression. Pull the plugs(one at a time) and stick you finger in the plug hole and have the engine cranked over. Does the pressure against your finger feel uniform in all the cylinders?

Do you have a source of compressed air and somewhere to buy a fitting that fits into the cylinder holes? You can make a home leakdown tester if so. One cylinder at a time, pressurise the cylinder and listen a hissing sound. This indicates bad compression rings or bad valves. If you hear hissing, pour a teaspoon of oil into the cylinder and repeat. Hissing gone? bad rings. Not gone? Valves.
We have a thread here that might help:
https://www.2carpros.com/articles/car-cranks-but-wont-start

Not that I've ever heard of. The only safety switch I can think of would be the fuel pump cutoff, but you said it's getting fuel. There's a clutch safety, but it's turning over.
Have you tried starting with the throttle open a bit?
If not, do so. It may be as simple as the idle being set too low.
Try spraying a little bot of starting fluid into the air intake. If that starts it, we can go from there to get it running and starting good.
If you can, look inside the valve cover to see if the rocker arms are moving. This is a horizontally opposed engine, so this might not be easy to do. If you can look in, but the rockers aren't moving, you have a timing belt issue.