The Deck "wood" post that is nailed on the cement foundation is rotten.
I understand there are synthetic deck materials made of some kind of plastic for the deck flooring.

Are there similar materials for the deck "wood" posts?
Is there a way to make the wood post resistant to rot?

The use of a proper post base between the wood and the concrete will help prevent rotting of the post. There are very cheap galvanized steel post bases that look awful, or more expensive cast aluminum post bases that look neat and will last longer. Both should be easily available from a good lumber yard.

The use of pressure-treated or decay-resistant ood, such as cedar or redwood, with a good post base will give you decades of good service.