There’s a difference between a cliffhanger and a to be continued.
Back to the Future 2 was a TO BE CONTiNUED because the plot of BTTF2 resolved. The stopped Biff and got the almanac. Then another problem shows up and teases part 3.
Star Wars by its definition is just chapters in a war story. The defeated the first Death Star but the Empire was still there. Luke got his training in the sequel but he took an L in his fight with Vader. That’s an ending though. Losing Han was an L, too but it was a conclusion.
Spiderverse didn’t actually resolve anything. Miguel is still after him, Spot is still after him, his dad is still in danger, and now he’s trapped on Earth42.
Edit: Gwen and Miles’ characters did change and since that carries the movie it feels like it progressed even though the plot was all build up.
Spiderverse wasn’t a cliffhanger. It really was half a movie.