Everything has been on backorder since COVID, it's no surprise. Manufacturers can't even get vehicles built, never mind supply replacement parts. If they can't fix your vehicle, you may be eligible to have Subaru take it back as a repurchase depending on your state. The only reason they have zero exhaust manifolds in their parts depots is because they're going through them due to failures, not because they didn't have the foresight to release the service part.