Food waste can be composted, and depending on how much oxygen is present, you can get methane out of it. But it's more common to use composting as a heat source and a fertilizer source. Same thing with human solid waste, you can get a decent amount of methane out of it and there are toilets set up to do this. I've seen standalone portable waste-to-energy toilets, and I've seen integrated facilities that directly help power a building.
I'm not familiar with what you mean by "cold plasma pyrolysis". Typically pyrolysis means you heat something up until in breaks down, and if it's flammable you do it in a deoxygenated environment. When you do this with plastics, you get mixed shorter-chain hydrocarbons, which can then be refined and used as fuel. There's plenty of easily searchable videos on DIY pyrolysis setups where there's a compartment where the plastic is put to be melted down, a compartment around it where the fuel burns, and a tube from the plastic compartment into a cooler place where it will condense and drip into a storage container. I think the setup I saw used around 40% of the fuel it produced to sustain/repeat the process.
Honestly, I think this is a much better fate for plastic waste than being left exposed to the elements to turn into microplastics. Yes, it turns plastic waste into carbon emissions, but the bigger question for carbon emissions is how much oil is drilled and how much energy demand we have in the first place. I'd say it's even a better use than recycling it into more single-use plastics.
Related to this is CHP (combined heat and power) machines, which can use different settings to produce different combinations of electricity, heat, and (biologically-inert, sequestrable) charcoal.
Making hydrogen gas is an extra step that rarely makes sense. Because it combusts without generating CO~2~, and because it's often made from CH~4~, it's kinda gimmicky and easily greenwashed. The only time you want to use hydrogen gas is when it would have a situational advantage over other fuels, which are more energy-dense and portable.
