lh_places_get_applicable_post_types: the candidate post types (public, excluding attachment). A type must also declare lh_places-geo_support.lh_places_validate_options: filters the Google Maps API key option before it is saved.wpgm_geoquery_srid and wpgm_known_capabilities: from wp-geometa-lib (see Spatial queries).lh_places_initial_run is a one-off event scheduled on activation (on every site when network-activated). It flushes rewrite rules and installs the spatial tables. Deactivation clears it.
There is no settings page of its own. An optional Google Maps API key field is added to GatherPress’s general settings and stored in the google_maps_js_api_key option. If it is empty, a key saved by The Events Calendar is shown instead. The key is only used for one thing: when a singular post contains the map block and has coordinates, the LH OGP plugin uses a Google static map as the post’s sharing image.
gatherpress_venue gets geo support automatically, and the API key field lives on its settings page._VenueLat or _VenueLng is saved, it is copied to geo_latitude or geo_longitude.lh_ogp_meta_tags_singular_og_images_filter filter, as described under Settings.