Twitter not being blocked on iOS
I have NextDNS installed with a configuration profile on an iOS device and have set up Twitter to be blocked. However, the blocking does not seem to work. Bot in Safari and the Twitter app Twitter is available.
I don't know about iOS but running the app on Android and it seems like they don't need DNS for basic tweets and messages to function. For me, using the Twitter option on parental controls blocks, images, videos and profile pictures that are from their CDNs and that's probably why they do a lookup. Seems like they either bypass or hard code all the other connections.
So it still brakes functionality but doesn't really block it completely.
I'd say doing a search for something or clearing the apps cache should show similar results on your end.
Overall, if they are getting past DNS, there is nothing to do really.