Hi @Johannsen, welcome to Thunkable! 
Be sure to check out our posts about How to ask Great Questions v2.0 and our Community Guidelines as you get started.
Most of this is dependent on the operating system and browser as opposed to anything programmable in Thunkable. For example, on iOS, links clicked from a webviewer will automatically open within the web viewer component. On Android, the link will automatically open within a new browser window. This is the default for Android and not something you can change within a Thunkable app.
Hope this helps!