Message notifications produce “This content can’t be displayed”

There are multiple "text"properties in the message structure. I believe the doc is referring to the top-level one outside all blocks definitions.

Example:

{
  "channel": "C1H9RESGL",
  "text": "Text here for notifications",
  "blocks": [
    {
      "type": "section",
      "text": {
        "type": "mrkdwn",
        "text": "Danny Torrence left the following review for your property:"
      }
    }
  ]
}