What’s the best encryption strategy to go with when everybody needs to be able to write data but only a select people can view it?

I really just need an encrypted support ticket system essentially. The user who writes the ticket doesn’t need to be able to view it afterward but a handful of staff need to be able to decrypt the data and view it. My backend is Firebase (using Firebase Authentication as well) and the users will be submitting information via the mobile app and the staff will be viewing the information on a web app. Ideally, the encryption/decryption would be done on the client-side.