As of August, 14th 2025, this is now possible using the table block:

{
    "blocks": [
        {
            "type": "table",
            "rows": [
                [
                    {
                        "type": "raw_text",
                        "text": "Header A:1"
                    },
                    {
                        "type": "raw_text",
                        "text": "Header B:1"
                    }
                ],
                [
                    {
                        "type": "raw_text",
                        "text": "Data A:2"
                    },
                    {
                        "type": "raw_text",
                        "text": "Data B:2"
                    }
                ]
            ]
        }
    ]
}

Sources:

• https://docs.slack.dev/changelog/2025/08/14/block-kit-table-block
• https://docs.slack.dev/reference/block-kit/blocks/table-block
• https://app.slack.com/block-kit-builder/T5ZDBJ69J#%7B%22blocks%22:%5B%7B%22type%22:%22table%22,%22rows%22:%5B%5B%7B%22type%22:%22raw_text%22,%22text%22:%22Header%20A:1%22%7D,%7B%22type%22:%22raw_text%22,%22text%22:%22Header%20B:1%22%7D%5D,%5B%7B%22type%22:%22raw_text%22,%22text%22:%22Data%20A:2%22%7D,%7B%22type%22:%22raw_text%22,%22text%22:%22Data%20B:2%22%7D%5D%5D%7D%5D%7D