Depends entirely on how you define the parameters of the question. Egypt has been around for a very long time, but is the ~3000BC Egypt the same country as the 2024 Egypt? Did Egypt stop being Egypt during the period of Roman rule? What about during Macedonian rule? Did people 5000 years ago even have a concept of a “country” that would align with what we think makes a country in 2024? Do people in 2024 even have an agreed upon concept of what a country is today? (I would say evidently not) Does the country of ancient Persia still exist? If it’s longest contiguous self-sovereignty then probably Japan would be pretty high up the list. If its longest surviving constitution, then the USA and San Marino would also be two of the oldest countries in the world. But is San Marino even a country? Certainly not by every single metric you could possibly use to define one. Is the Magna Carta still in effect? Some of it is, but is that enough to make it the oldest surviving constitution?

To make the question meaningful you probably have to make it a lot more specific. Otherwise the answer is just a debate about what constitutes a country, and what constitutes it coming into and out of existence.