Training vs test data set for supervised learning in real life scenario

Question

In the tutorials, I have noticed only similar data has been used with models training and prediction.

I was wondering how cases where you can't find training data that is similar to your final use case(test data)?

What happens if I am building a recommendation system for house rentals but the closest training data I can find is for movies. And it has fewer features than I would have in the house scenario.

How common are scenarios like this and how are they generally handled?