How to use Source in ElasticSearch Net

How can I project fields in the Elasticsearch Net 8?

I tried:

SourceFilter filter = new SourceFilter();

filter.Includes = new List<Field>() ..  hm not the way

SourceConfig sourceConfig = new SourceConfig(filter);

SearchResponse<PostDocument> searchResponse = await client.SearchAsync<PostDocument>(s => s
.Index(index_name)
.From(page)
.Size(countPerPage)
.Source(sourceConfig)
.Query(..)

Try 2

.Source(null).Fields(
 fs => fs.Field(f => f.Id),
 fs => fs.Field(f => f.PostId),
 fs => fs.Field(f => f.Title))

I also saw SourceIncludes which takes in Fields but its not an expression same as the chain Fields

Any help? docs is still very limited

Dicussion mentioned here with possible answer

Infer.Fields(x => x.SomeField1, x => x.SomeField2)

Is indeed the correct syntax to use in this case.