Does iPhone 13 contain the U1 chip?

Even the iPhone 16e – which lacks Ultra Wideband support – is "AirTag compatible" in a very limited sense. But having an Ultra Wideband chip means that you can use "Find Nearby" and "Precision Finding" once your iPhone gets within Bluetooth range.

Use AirTag and Find My to keep track of your personal items - Apple Support

iPhone 13 models generally support Ultra Wideband capability except on a handful of countries where local laws, or international regulatory requirements, require it to be turned off. E.g., if you're in Russia, that feature would be turned off.

Ultra Wideband availability - Apple Support

If by "U1", you mean an "Apple Ultra Wideband chip", the iPhone 13 contains one of those.

Some current Phones have an "Apple second-generation Ultra Wideband chip" and there are other models (e.g., the iPhone 16e) that do not have an Ultra Wideband chip at all.