Yeah, I bought my Mappa puffer when he was around 9-10 inches long in April of 2019, I put him in a deep 120 gallon (smallest dimension is 24") and he has already outgrown it. He is around 22-24" long now, and I am in the process of designing a new tank for him and his 3 tankmates. I would say a 300-gallon tank would be ok.
Here is a video of Puff Daddy eating at the end of a video, skip to 15:19 in the video:
This was about a year ago when he was around 20" long: