Get all items based on specific column, can't get more than 25 records?

You can pass a ‘limit’ argument to the items_page query, i.e:
 

query {
  boards (ids:1234567890) {
    items_page (limit: 50, query_params: {rules: {column_id: "timeline", compare_value: ["2023-06-30", "2023-07-01"], compare_attribute: "START_DATE", operator:between}}) {
      cursor
      items {
        id
        name
      }
    }
  }
}