Below code:

package data

import (
    "context"
    "encoding/json"
    "fmt"
    "time"

    pgxmock "github.com/pashagolub/pgxmock/v3"
)

type Timestamp struct {
    time.Time
}

type Model struct {
    Column1 string      `db:"col_1_name"`
    Column2 Column2Type `db:"col_2_name"`
}

type Column2Type []*T

type T struct {
    ID        int       `json:"id"`
    CreatedAt Timestamp `json:"created_at"`
}

func F() {
    const tableQuery = `
-- query 
SELECT
        col_1_name,
        col_2_name
FROM table1;
`

    mockDBSetupFunc := func(m pgxmock.PgxConnIface) {

        t, _ := time.Parse("2006-01-02T15:04:05", "2024-06-25T04:33:55")

        // helper to fill column 2
        getColumn2 := func() []byte {
            c := Column2Type{
                &T{
                    ID:        2,
                    CreatedAt: Timestamp{Time: t},
                },
            }
            b, err := json.Marshal(c)
            if err != nil {
                panic(err)
            }
            return b
        }

        m.ExpectQuery(tableQuery).
            WillReturnRows(pgxmock.NewRows([]string{
                "col_1_name",
                "col_2_name",
            }).AddRow(
                "4432",
                getColumn2(),
            ))
    }

    mockDb, err := pgxmock.NewConn(pgxmock.QueryMatcherOption(pgxmock.QueryMatcherEqual))
    if err != nil {
        fmt.Printf("failed to set up fake db: %vn", err)
        panic(err)
    }

    mockDBSetupFunc(mockDb)

    rows, err := mockDb.Query(context.Background(), tableQuery)
    if err != nil {
        panic(err)
    }
    defer rows.Close()

    for rows.Next() {
        var model Model
        if err := rows.Scan(
            &model.Column1,
            &model.Column2,
        ); err != nil {
            panic(err)
        }
        fmt.Println(model)
    }

}

gives error: panic: Destination kind 'slice' not supported for value kind 'slice' of column 'col_2_name' on rows.Scan()

Why mismatch on second member type in Model? on invoking below code:

package main

import (
    "github.com/a/b/data"
)

func main() {
    data.F()
}