Polystyrene is relatively easy to depolymerize with enzymes, catalysts and moderate amounts of heat, see

https://pubs.acs.org/doi/10.1021/acssuschemeng.1c08400

The pyrolysis route they are using can be problematic because it produces carcinogenic aromatic compounds like

https://en.wikipedia.org/wiki/Benzopyrene

which has a metabolite which is almost a cancer-causing drug. In principle you could pyrolyze plastics all the way down to carbon monoxide + hydrogen syngas and then build that up to molecules you want with C1 chemistry

https://en.wikipedia.org/wiki/C1_chemistry

but most of the people who are trying chemical recycling by pyrolysis are trying to cook the molecules partially so the output fuel is a witches brew rich in hazardous aromatics. There is a lot of research into cleaner processes for chemical recycling such as

https://www.nature.com/articles/s41598-021-83659-2

and that one at the top but every large scale plant I've seen is a pyrolysis plant that's had to fight with environmentalists to start operations. From the viewpoint of a chemical engineer making fuel is for the birds because gasoline costs 50 cents a pound and (almost) any other chemical costs a lot more than that.