Relay and wifi module

Since there's enough "smart" switches that do that, the answer is clearly that it's possible. That answers your question, but let's be helpful instead of just correct:

You still shouldn't do that: when you use an external power supply, someone who knows electronics makes sure you're not getting killed. Building a 230 V switch-mode power supply isn't trivial, and so you'd either buying a industrial module (more expensive than a whole commercially available smart switch, or an external 5V supply) or building something that's dangerous if you have no education on building safe circuitry and a good understanding of electronics.

When you build this into your own design, it's your fault if you get electrocuted or your house burns down in your sleep. As a beginner's project maybe do something that doesn't involve 230 V; you're not building this for any productive usage, anyways. (if you plan to do exactly that: don't. A commercially available device would be much much cheaper due to the economics of scale than an equally safe device that any of us could build ourselves.)