Vakarta is a website that can also be an app.
You need to be vaccinated more than once, but not every day. Therefore, it makes no sense to take up tens or hundreds of megabytes of your smartphone. In addition, modern technologies allow you to create PWA (Progressive Web Applications) that take up very little space and are fully perceived by devices.
The Apple AppStore version is also planned (not soon).
In any case, for iPhone and Android you can install the Vakarta app in a couple of clicks. Follow the simple instructions for your browser.
Vaccination is easy.
Create a personal vaccination calendar