Adding some personal analysis to your point, the last time I looked at plastic market research in detail, the two biggest markets by volume and revenue were packaging and insulation, which I believe were dominated by thermoplastics. Those are the big ones if you want to make an impact on plastic usage.

Also, pulling from memory that may not be quite right, but I recall roads taking a substantial amount of polymer additives and that tire degradation is a major source of microplastic exposure for humans. The tire problem is poised to get worse with EVs being so heavy and accelerating so hard that the tires are bigger and wear faster, but I'm not aware of even any promising research there besides more bio-based feedstocks to improve the sustainability.