And as one comment in the linked GitHub issue states, calling their license "open source" is really more of a marketing joke. Although the seem to have changed their restrictive license [1] to the GPL License [2]
Edit: Although its not the official apps, its heavily used by some official instances such as the health departments of some cities/states. The Luca app is financed by those departments purchasing a license. According to news, some licenses cost around 440k€ of taxpayer money [3]
[1] https://gitlab.com/lucaapp/android/-/commit/a30432ec4a01c2ca...
[2] https://gitlab.com/lucaapp/android/-/commit/4433884f00462bae...
[3] (German) https://www.faz.net/aktuell/politik/inland/mecklenburg-vorpo...