The Trimurti, although it does exist in Hindu scripture, isn't that important for most Hindus. It was brought to the encyclopedias of the west by non-Hindus who were looking for something comparable to the Christian trinity. So, in reality, it's not very common at all, but if a newcomer looks in Britannica or World Book, it'll be right up front.
In Hinduism, the Supreme god in each sect does all 3 of these aspects ... creation, preservation, and destruction. These are all poor translations, again made by non-Hindus. Much more accurate word, in my view, are emanation (issuing forth), sustaining, and dissolution (withdrawing). So in my sect, Siva has 5 powers (graces) ... emanation, sustaining, dissolution, revealing, and concealing. Similarly, in Vaishnavism, Vishnu (or Krishna, or Rama) Vishnu does it all. Same for Shaktites.
Of course there is also overlap, and various seemingly endless combinations of ideas.
If it was me you were referring to, I don't believe in a creator god separate from his creation, (which is the more western way of perceiving creation) but I do believe Siva emanates. He is All and in All.
Yes, some people also believe in the trimurti and classify people accordingly. That's not a very common sense of it, but it is there.