After much trial and error, I think this works with the following:

1. set css height to a pixel height on the container element of the capacitor-google-map component (in my case an ion-content element inside an ion-grid)
2. set css position: static !important on the capacitor-google-map component

This seemed to fix the problem with displaying a google map in a modal page using Ionic 7 with Angular and Capacitor 6.