Great alternate method.
The only thing you might be doing wrong is pressure-cooking. Let me explain:

Cannabis has multiple compounds. THC (THCA before decarboxylation) is most known for its psychoactive (and mostly because it's dominant), CBD (CBDA) has been discovered and is being fully researched since few years. but there are around 400 cannabinoïds in there.

Decarboxylation process:

It is basically the effect of heat on molecules pushing them to release a carbon atom from the chain (or in other words, the "A"cid reacts with the carbon chain and is removed from our primary matter): E.g. THCA transforms to THC after decarboxylation. same goes as well for CBDA/CBD and others...

This is to say that you need to pay close attention to temperature as it is different temperatures for each of the molecules.

To name few:

**THCA to THC : between 100°C (212°F) and 157°C (314°F). The lower the temperature, the more time it needs to completely decarboxylate.

**CBDA to CBD : around 180°C/220°C (360/428°F)

Here's chart that might help you see the relationship

According to all my researches and experience though (more than 4 years), when you see Aged in the chart above can mean also overheated

You can transform THC to CBN if you overheat it and surpass the decarboxylation window. E.g : THC 100°C (212°F) and 157°C (314°F)

The best way I found so far is to use :

*a rice cooker, as advised by Rick Simpson: This keeps the temperature from rising above the threshold.
*A Infra-Red temperature sensor to monitor the temperature (especially at the last stages when few alcohol remains)
*You can recycle your alcohol by distillation and recover it back as well

If you don't wanna buy a rice cooker (around 30 bucks), you can do a water bath:

Water bath process: (