Plumbing. So much plastic in fixtures, pex, pumps, the rubber hoses that are rubber anymore, shower heads, toilet seats, filter housing, filtration media itself, drain pipes, seals, etc.

Insulation is disgusting. Rockwool is about the only bat type stuff I'll ever use. Foam is awful, even the soy-based ones. Better to use thickness of stone or brick than use most modern insulation. My plan is to use hempcrete for all the exterior walls. Three ingredients. DIY friendly. Then plaster over it with simple, undyed lime plaster.

Flooring is all sorts of awful.

Siding. I'll avoid it entirely.

Venting/fans.

Lighting. (LEDs use a lot of cheap plastics.)

Laminates.

House wrap.

Asphalt shingles.

Coatings on things like steel roofs can sometimes be plastics.