Once you have created a database Running PostGIS in Silverblue you may want to import data to it.
For example, to import the data from: https://github.com/microsoft/USBuildingFootprints?tab=readme-ov-file. You can run this from the container’s CLI:
ogr2ogr -f "PostgreSQL" PG:"dbname=nys_tax_parcels user=postgres" \
"/tmp/us_building_footprints_new_york.geojson" \
-nln ny_building_footprints -nlt POLYGON \
-lco GEOMETRY_NAME=geom -lco FID=ogc_fid