Questions & Answers about Mi amigo es bienvenido aquí.
In modern Spanish, possessive adjectives like mi, tu, su, nuestro normally replace the article. So mi amigo means my friend.
Using el mi amigo is not standard in normal modern Spanish.
Spanish normally uses ser in this expression: ser bienvenido = to be welcome.
Here, the sentence is talking about your friend being accepted or invited in this place, not about his physical location or a temporary condition. That is why es is used.
So:
- Mi amigo es bienvenido aquí = My friend is welcome here
Using está here would not be the normal choice.