The DApp browser has been removed from the iOS version of Trust Wallet in order to comply with Apple AppStore guidelines. See the official announcement here: Trust Wallet removed DApp browser to comply with Apple App Store guidelines
In order to allow DApp developers to see how their DApps function on iOS, we have made the browser available with the following steps.
In this guide we will show you how you can re-enable the built-in DApp browser in just three easy steps. You need to have version 5.11 or higher installed on your device to proceed.
Open Safari Browser and then type in the URL: trust://browser_enable, then tap on Go.
A prompt will appear that will ask if you want to Open this page in “Trust”?, tap on Open.
Make sure that there is no open tabs on your Safari browser when you type the URL in order to see this screen.
The Trust Wallet app will launch and the DApp browser will be enabled.