Many popular online services with an iOS app can open links directly within their app automatically. For instance, tapping an Amazon link opens it directly within the Amazon app. However, there’s no way to control this behavior, and you may want to explicitly go to the page that the link points to, or even use a different app entirely.
Opener ($1.99) is a clever iOS app that gives you more control over how links are opened. You can either copy a link to the clipboard and then launch Opener, or use the action extension in the Share Sheet, and select from a list of apps that the link can be opened in, making it much easier to open links in third-party apps.