Yes - here is your evidence, specifically about Puerto Rico. They ARE US Citizens, but they CANNOT vote in US Presidential elections.
No, residents of Puerto Rico, as U.S. citizens living on the island,
cannot vote for the U.S. President in the general election because Puerto Rico is a territory, not a state, and only states and D.C. have Electoral College votes. However, they can participate in the
presidential primaries and can vote in the general election if they move to one of the 50 states or Washington, D.C