❌ I saw a beautiful dream last night
✅ I had a beautiful dream last night
have a dream normally we say ‘I have a dream’, if you are talking about something that you are hoping for in the future.
If you are just talking about what happens when you are asleep, we simply say ‘I dream every night’ or ‘Last night I dreamed/dreamt about my old home’. If you are talking about a specific dream when you were asleep, say ‘I had a wonderful dream last night’