I happened on this thread Googling, for the same reason as Kashyap.
I can’t really confirm or deny from the deep reading of Shopify docs that I can create a Custom Pixel from an App like I would an App pixel. The lax sandbox is the main thing I am interested in, because we need to load a tracking library, as in the Custom Pixel examples, but I have never seen an example of doing that with an App pixel.