Custom Formatter for Read-Only Fields conditional based on other columns

This looks like a limitation of SharePoint column formatting rather than the IF syntax itself. The readonly property in fieldsettings doesn’t appear to support dynamically evaluating the current viewer ([Me]) against a Person field.

Also, [me] isn’t a valid column-formatting token for getting the current user’s email.

If you need the field to be read-only depending on who is viewing the item, you’d generally need to handle it with permissions, Power Apps, or custom SPFx/JavaScript rather than conditional readonly formatting.

If anyone has found a way to achieve this purely through fieldsettings/JSON formatting, I’d be interested too.