This is how Mica and I have arranged for scritches. It wasn’t me specifically training this behavior, but a combination of us working together to find something she is comfortable with.
She’ll let absolute strangers pet her like this as long as they do it right. You can see she’s not quite comfortable, though, she’s still alert and looking around. I don’t think she’ll ever be as snuggly or friendly as some cockatiels, but she isn’t mean and she does like scritches. They just have to put on her terms.
I have no idea why she likes to pick the training perch. None of the other birds do it.