For anyone using #Raivo OTP: I've just found out the developer sold it to a sketchy company. The application was not updated since then, but, as iPhone does not allow pinning to a specific application version AFAIK, I've decided to switch to Ente, which is open-source and secure enough as well (it requires an account for backing up to their cloud, but everything is locally encrypted). Not sure if it's the best solution, but that's the status quo.