The AsyncSession object in the Neo4j's official .NET driver has a ReadTransactionAsync method that you can use for marking read queries explicitly.

For Version 4 of the driver, the below example using the ReadTransactionAsync function is correct:

private async Task GetActors(IAsyncTransaction tx, string title)
{
    var result = await tx.RunAsync("MATCH (p:Person)-[:ACTED_IN]->(m) "+
"WHERE toLower(m.title) CONTAINS toLower($title) "+
"RETURN DISTINCT p.name as actorsTx", new { title });
    while (await result.FetchAsync())
    {
        var record = result.Current;
        Console.WriteLine($"{record["a.name"]} knows {record["b.name"]}");
    }
}
public async Task GetMovieActors(string movieName)
{
    using (var session = Driver.AsyncSession())
    {
        await session.ReadTransactionAsync(tx => GetActors(tx, movieName));
    }
}

For Version 5 of the driver, you need to use the ExecuteReadAsync function instead:

private async Task GetActors(IAsyncTransaction tx, string title)
{
    var result = await tx.RunAsync("MATCH (p:Person)-[:ACTED_IN]->(m) "+
"WHERE toLower(m.title) CONTAINS toLower($title) "+
"RETURN DISTINCT p.name as actorsTx", new { title });
    while (await result.FetchAsync())
    {
        var record = result.Current;
        Console.WriteLine($"{record["a.name"]} knows {record["b.name"]}");
    }
}
public async Task GetMovieActors(string movieName)
{
    using (var session = Driver.AsyncSession())
    {
        await session.ExecuteReadAsync(tx => GetActors(tx, movieName));
    }
}