is the the spring festival a bad time to travel given what I want to do?

Never been to China and I want to hit Shanghai, Chongqing, and Chengdu in a span of 2 weeks while also experiencing known festivials China has to offer

I was doing research, and I saw that Shanghai has the Yuyuan Garden (Yu Garden) Lantern Festival and Chengdu has the Panda Lantern Festival, which caught my interest as these events overlap

However, while scrolling reddit and youtube, I'm seeing people advise against CNY as there's huge migration of people and trains can be extremely crowded or sold out and they also say there's a period of time where things are a ghost town

Trying to ask advice here, a bit confused as my understanding is that festivities like the two lantern festivals I mentioned should be crowded and not a ghost town no? but I'm confused what dates in particular are things a ghost time and what dates in particular I should avoid traveling between cities and when the huge migration of people happens?