I don't know in what country you are, but mine (the Netherlands) has open-sourced everything around the corona-check apps, including backend, design, etc. on Gi

I don't know in what country you are, but mine (the Netherlands) has open-sourced everything around the corona-check apps, including backend, design, etc. on GitHub (https://github.com/minvws https://github.com/minvws). If you or your granny aren't good at reading code, you just have to trust that other members of the public who are would have made some noise in the media if something fishy was going on.