Command aggregate failed: $geoNear, $near, and $nearSphere are not
allowed in this context, as these operators require sorting geospatial
data. If you do not need sort, consider using $geoWithin instead.
Check out https://dochub.mongodb.org/core/near-sort-operation and
https://dochub.mongodb.org/core/nearSphere-sort-operationfor

await db.Users.Indexes.CreateOneAsync(new CreateIndexModel<DE.User.User>(
Builders<DE.User.User>.IndexKeys.Geo2DSphere(u => u.Location)));
    
    
double distance = req.Distance.Value * 1000; // km to m
var filter = Builders<User>.Filter.Near(u => u.Location, req.Longitude.Value, req.Latitude.Value, distance);
 query = query.Where(user => filter.Inject());