The boiling method, and using ultrasonic devices so far sound promising:

https://projectboard.world/isef/project/eaev062t-harnessing-ultrasound-for-microplastic-filtration

Neither method is 100%, and sadly even if it were, there is no way to avoid ingesting microplastics. It's basically in all food sources at this point. Any animal, or plant have them in them, and those sources are going to be exposed to them; even rain has microplastics in it now.

I suppose the best way to actually avoid microplastics in the food chain would be growing plants in a greenhouse type environment (with dug up deep pre-plastic dirt?) only using properly treated water? For meats, I guess lab grown meat would be the way to avoid it, using plastic free (or less) sources for material?

I've actually been throwing out old spices in recent years, but maybe I should be saving them. Maybe they are the last vestiges of plastic free spices, and will be worth a fortune to paranoid rich people that want flavor?