Bad technique on unserious learning can still lead to serious injuries like RSI.

Proper technique is also important so that playing is actually fun and not painful. Even just a few lessons on how to properly sit, how to avoid tension in your hands and so on can go a long way. There are video lessons that explain that stuff as well but you need to be very disciplined and really repeat these lessons over and over.

You can absolutely self-learn the piano. People that genuinely don't have the money for a teacher shouldn't let that stop them but it absolutely is harder. Set yourself up for success if you can.