I feel that there are many possible solutions, however I can understand the frustrations faced by the teenager. We are all going through an unprecedented period in history and with schools, universities and institutes closed and exams being cancelled or being moved online for the foreseeable future, a lot of students have lost motivation.
I work closely with students of all ages and abilities, studying various curricula and keeping them motivated and occupied has been something we help with. I would recommend the teenager signing up to online courses in subjects that they are interested in or would like to learn more about. Edx.org is a fantastic platform that offers a wide range of courses that can be completed over a short period of time and many of these courses are free. This would not only engage the student but the fact that they are free would make it easy for them to change courses if they do not enjoy it. These courses would also give them an insight into career paths they may be interested in, and many of the courses do not require any prior knowledge. They would also be a fantastic addition to any CV, cover letter or application in the future.
I would also recommend trying some vocational or hands-on activities that could be useful or fun. These could range from cooking, to building things or pottery and art. Initially the student may seem uninterested but as they find something they enjoy, naturally they would want to excel and improve.
Having all this time off could be seen as difficult as it could demotivate students and cause them to be idle, but it could also be a great time to practice new skills which would be helpful not only for applications but also essential life skills such as cooking. It could also allow students and teenagers to find new areas of interest whilst staying safe.

I would be more than happy to discuss this with you further.