Capacitor Google Maps Plugin map showing in ionic serve but not on device

Capacitor
1

Ionic Angular app.
I installed and configured Capacitor Google Apps Plugin.
Ionic serve shows the map but npx cap open android doesn’t on the device. Android Studio says no problems in the IDE.
The App Inspector shows a single message in the Database Inspector: “ue3.db (closed)”. Then, it specifies “Can’t open offline database /data/data/ch.swissthai.map1/databases/ue3.db”. ch.swissthai.map1 is the appID. I’m not knowingly using a database so I presume this is a function of the plugin.
In the docs, Variables are mentioned as being used by the plugin. They don’t show in Android Studio/variables.gradle. If I add them as they are named into variables.gradle the app cannot be compiled because they “are not variables”. If I just use the first part like "googleMapsPlayServicesVersion = ‘18.1.0’ outside the ext{}-paragraph: compilation error. Inside ext{}, they have no effect: don’t show in Android Studio’s variables.gradle file.
What can be done?

2

OK, it was about visibility as they say in the docs. In the test app the map appears after some time. The .scss file is as follows:

html {
  background-color: transparent;
}

ion-content {
  --ion-background-color: transparent;
}

#container {
  background-color: transparent;
}

capacitor-google-map {
  display: inline-block;
  width: 275px;
  height: 275px;
}

Now, when I want to integrate the map into the real app, it doesn’t show any more. This probably is because of the black background set in theme/variables.scss:

:root {
  --ion-background-color: #000;
  --ion-text-color: #fff;
  --ion-toolbar-background: #000;
  --ion-toolbar-color: #fff;
}

I can’t counter this setting in the local ,scss file like:

:root {
  background-color: transparent;
}

ion-content {
    --ion-background-color: transparent;
}

as recommended in the Plugin docs.
Cam somebody help here please?