Attached is a video of me taking off, shifting from first to second, then applying full throttle. Power felt sluggish and after reaching \~5000rpm it began to cut off, almost felt like a more aggressive redline. This only starts to happen after \~40 minutes of driving.

The car has done this in the past. But after sitting for a few months with the battery disconnected the issue seemed to resolve itself until last night (after about 5 days of driving). Both last night and when the car was doing this months ago, switching the car off then on again will resolve the issue for about 5-10 minutes before it becomes present again. When the car used to do this it was much more aggressive and typically I couldn't exceed about 70km/h (43.5mph) at 3000rpm in any gear.

I was told it was likely related to the catalytic converter. I checked both recently and visually they both appear okay from the inlet end.

I am yet to 'scan' the car as I am admittedly a little intimidated by early OBD systems, but I will obviously do so if necessary

1997 Subaru Forester, 5sp manual, early EJ20J, \~280,000km (174,000 miles).

Has had rust in the fuel system due to sitting for years before me purchasing the vehicle, but I have done my best to completely clean and treat the fuel system and only use premium fuel

Any ideas?

1997 Subaru Forester, low power and won't reach redline