Apple intelligence unavailable in iPhone 15 Pro even after updating to iOS18.1

Have you read the link below on how to get Apple Intelligence and you've changed your language to US English as well as US English for Siri? Also check the model number of your iPhone in Settings > General > About > Model and if it says CH/A, that means the phone was manufactured for the China market, and it won't get Apple Intelligence, regardless of Language or location until it is approved to be used in China.

See here for more details --> How to get Apple Intelligence - Apple Support (CA)

well it's not available in all countries

List of countries where Apple Intelligence will be available