Dear Mark_Reynolds_1066,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
As per your description, please let us cooperate and please don’t worry, we can work together to narrow down and resolve the situation.
Based on my test, to display the SharePoint date format as dd/MM/yyyy, the JSON code, below can work:
{
"$schema": "https://developer.microsoft.com/json-schemas/sp/v2/column-formatting.schema.json",
"elmType": "div",
"txtContent": {
"operator": "toLocaleDateString()",
"operands" : ["@currentField"]
}
}
Result:

Also, to display the SharePoint date format as dd/MM/yyyy, you can also use the SharePoint calculated column instead of using JSON column formatting:
Steps:
1.Create a new calculated column with the below formula to format date with

2.Click OK, then go back to your List, you should note that the Date column format is now displaying in dd-MM-yyyy as below.

Your understanding and patience will be highly appreciated. I hope that you are keeping safe and well!
Sincerely,
Waqas Muhammad