it depends whether you are constructing this structure for a reason - for example, do you then pass this message to a particular node that expects this format?
When you stringify the property then the
payload.options.reply_markup property is a single string. It doesn't have properties and you can't directly address the values inside it.
But if you are generating this message yourself in a Function node, then why do you need a Switch node to route it? Your Function node could have multiple outputs and you could add the logic in the Function node to choose which output it is sent on.
Without more information about what your wider flow looks like, its hard to be more specific.