Call to undefined method Drupal\search_api\Plugin\views\query\SearchApiQuery::addWhereExpression()

Problem/Motivation

search_api_location README claims Apache Solr and Geofield is supported, but in practice I get an error "Error: Call to undefined method Drupal\search_api\Plugin\views\query\SearchApiQuery::addWhereExpression() in Drupal\geofield\Plugin\views\filter\GeofieldProximityFilter->opSimple() (line 278 of /app/web/modules/contrib/geofield/src/Plugin/views/filter/GeofieldProximityFilter.php)."

I have a Geofield indexed into Solr with type="Latitude/Longitude". I have a view based on the Solr index, and want to add a proximity filter. The filter UI has operator "Is less than or equal to" 50, with Unit of measure=Kilometers. Proximity Definition Mode (Source of Distance and Origin Point)="Manual Origin (Default)". The views preview errors with a an AJAX error, HTTP 500 in the backend, with "Call to undefined method" as mentioned above.

It appears that search_api assumes the backend is SQL instead of Solr.