I did add the list from the first reply, and figured out by trial and error which domains are required for essential features to work (which for me is sending and receiving messages and media, and viewing my friends’ stories), and found no way of blocking the ads without losing some of those basic features. I even managed to prevent friends’ stories from loading with ads still playing inbetween, but not the other way around.
as for other domains that aren’t on the list, it appears to connect to
europe-west1-gcp.api.snapchat.com for example, but given that
us-central1-gcp.api.snapchat.com are, as far as I can tell, required for the app to work properly, I assume that one is as well.