How do Date columns works?

I am learning Kysely from the website, at the getting started section I can see the following line:

modified_at: ColumnType<Date, string | undefined, never>

modified_at: ColumnType<Date, string | undefined, never>

But

ColumnType

ColumnType

is type-only and should not affect runtime conversion, how does Kysely knows when to convert the data into

Date

Date

in runtime?

How do Date columns works? - Kysely