I think that’s too broad of a question. There are hundreds, maybe thousands, of different plastic polymers, each with its own properties. Some a recyclable, some are not. Some are rigid, some are flexible.
Some plastics really are irreplaceable with anything else; other items could only be replaced with things far more expensive. Take things like one-use sterile equipment in a hospital—some things could be manufactured in stainless steel, but that causes other issues like sterilization and packaging for reuse, which is also not environmentally friendly.
Yes, we could get rid of or reformulate some percentage of plastic stuff. But probably far less than you would hope.