Could humans ever terraform Mars?

The short answer is: maybe in principle, but not with current capabilities.

Humans could someday try to terraform Mars, but it is a hugely difficult problem and any full-scale transformation would almost certainly be a very long-term project. Mars is currently cold, dry, and has a thin atmosphere, so people would need substantial engineering just to make the planet more habitable. A serious terraforming plan would likely involve warming the planet, increasing atmospheric pressure, protecting it from radiation, and building up breathable oxygen over a very long time.

Proposed ideas include orbital mirrors, releasing greenhouse gases, importing volatiles, or creating some kind of artificial magnetic protection, but these are still speculative concepts rather than near-term engineering plans.

A practical reality check is that Mars may not have enough readily available material to make it Earth-like just by using local resources, so any real attempt could require technologies and infrastructure far beyond what we have today.

So: yes, possibly in principle — but not with current technology, and not anytime soon.