Summary

Create a new custom list, you will notice this new list will have the following message as shown below.

An image.. + “Welcome to your new list” + “Select the New button to get started”

This post should help you to hide the welcome message.

Step By Step Solution

Step # 1: Create a column hideWelcome Yes/No Type and default value as No.

Step # 2: Add a dummy first row with hideWelcome as Yes for this row.

Step # 3: Add the View Formatter JSON code for the trick.

{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/row-formatting.schema.json",
  "hideColumnHeader": true,
  "hideSelection": true,
  "debugMode": true,
  "rowFormatter": {
    "elmType": "div",
    "style": {
      "display":  "=if([$hideWelcome], 'none', '')"
    },
	"children": [
	  {
		"elmType": "div",
		"txtContent": "[$Title]",
		"style": {
		  "flex-grow": "1"
		}
	  }
	]
  }
}

The first row with the hideWelcome as Yes will hide the welcome message.

Conclusion

The above trick may not work for all scenarios. As I have not tested all scenario. This is a technique to hide the welcome message based on the hidden field named hideWelcome.