I really want to do a PhD. However I have no clue to as to how to chose a topic. Do I choose something that interests me or do I choose something that is the need of the hour ? For example the need of the hour is related to technology or AI or environmental. However I have no interest in these. How do I chose a topic that satisfies both ??

You don't understand your interest area well enough if you don't know why it is (or is not) the need of the hour.

Read up (this is called a literature survey) and then look for interesting problems to solve (or knowledge gaps) in the area of interest. Usually, good research papers conclude with a section called "limitations of current work". These will trigger new ideas. Remember, a Ph.D. is a degree you should ideally complete in 4 years. Don't have any romantic ideas that you are out to solve the world hunger problem. Choose a problem (and a supervisor) so that you can complete the work in the assigned time. Be clinical about it.