How does a Recommender System recommend movies to a New User?
In general, a safe default option for recommender systems is to recommend the most popular product, so two options for the recommendation:


simply recommend the most popular movie in a time window around the current moment (maybe taking into account momentum),
do the same but marginalizing over account info, e.g. age, gender, country, language; also, IP location is an option to get such type of info.


Confidence assessment can be done based on recommendation success rate over the results of the same recommendation to previous users with the same profile characteristics, if such data is available.