I am using Xcode 13.1 and Monterrey 12.0.1. I created a Sticker App over the weekend, just a few sticker images to test and experienced the above error and cannot see the sticker images not on Simulator nor on an iPhone attached.
But, when I added the full set of iMessage App icons, clean build, it works fine. I still have the "StickerPackExtension[41845:1484263] [PPT] Error creating the CFMessagePort needed to communicate with PPT" but this is probably rehearing.
So my conclusion probably lies to Sticker App with Xcode 13 for some reasons require the the App icons to be there in order to see the Sticker images. This behaviour is different from previous Xcode version. 🤷🏻♀️
CM