I'm not sure on the copyright status of the TPT icon, but I can say it was created over 10 years ago, and whoever created it isn't active in the community anymore. There definitely won't be any youtube strike or similar issues from using the icon.

TPT icon can be found here: https://github.com/The-Powder-Toy/The-Powder-Toy/tree/master/resources/icon
Android icon is here: https://github.com/jacob1/The-Powder-Toy/blob/c%2B%2B/icon.png
(No copyright here, created by @LBPHacker)

Just be reasonable when you use it.