Pure synthetics can and should be applied to non-porous trim pieces - rubber, metal, mirrors, glass, headlights, taillights. They protect far longer than any products "designed" for rubber/vinyl.
Should you get any wax on porous trim, use an old toothbrush and peanut butter. It's an old detailer's trick.
You always want to apply a sealant - period. A true sealant serves a purpose - to protect.
It's your choice whether you want to apply a carnauba or not. Please don't use generic recommendations to finish with a carnauba - it's bad advice. Live in Arizona? Using carnauba is stupid. Is your car stored in the sun 24/7, a daily driver and you don't like waxing? Carnauba is not for you. Enjoy waxing a lot, dark color, not extremely hot environment? Carnauba. It should be used situationally dependent onc color, environment, daily-driver or non, garaged on open, how frequently you want to wax, how much you want to spend, etc.
I choose not to use carnuaba. I think the difference between a synthetic and carnauba is negligible and not worth applying carnauba once a month or more. Nor do I have time between three jobs.
I never apply a carnauba to a customer's car. They wont notice the difference between a synthetic and carnauba unless I did half and half and pointed it out to them. Even then they would say "Oh yeah, it is
slightly blacker on that side."
They just want a shiney, clean car. I use a nice sealant that takes less time to apply and I'm on my way.
