Can’t query a table for a distinct list using Dapper Wrapper – Fast crud

This is for C#, debug on Visual Studio 2022, backend database SQL server.

I am trying to get a distinct list of dates from a large table, so in TSQL I would have done:

SELECT OpenDate FROM dbo.TicketHistory

But I want to use Dapper Wrapper – Fast Crud, so I tried the following:

var distDates= cnn.Find().DistinctBy(options => options.OpenDate);

But I get an error: Invalid column name
and when I click debug error window “View Details” I get $exception “Internal error in the expression evaluator.”

Any help is appreciated!