Twin over queen size loft bed with desk are usually quite difficult to find for several reasons that tend to be self-defeating the point of actually getting a this type of furniture for practical reasons.
Buying a twin over queen size loft bed with desk was traditionally so that instead of two children taking up two rooms they could both comfortably occupy one room while having their own bed. This was usually so a lot of room could be saved within the house allowing perhaps an older sibling or some related adult to be in the other room. But seeing as you’re adding a twin over queen size loft bed into the equation you’re already taking up a lot more room than is necessary. Seeing as they’re generally for small children a regular size version is completely fine, having a much larger bed which is designed for adults seems unnecessary.
I think there are definitely some uses however, such as if you think the children will be bunking together for a long period of time and into their teenage years. Usually when children hit puberty they get moved out into their own room, and by this time the family has bought a bigger house or another room is freed up. But if you think that your children are going to be in that one room for a long amount of time then it is plausible that you’d want to make them as comfortable with twin over queen size loft bed with desk in there.