Two options that might work for you. Here’s a doc with both variants in separate sections. https://coda.io/d/Select-All_dThShGcGQc6/
Option 1
Convert the single-select into a multi-select, which then presents an option called “All”
Option 2
Use a single-select, but update the filter condition on your table to deal with the case where there’s no value selected in your single select.
In the picture below, Fruits is a table, and the single select on the canvas is a control named “FruitSingleSelect”
Thanks,
Hari.