There are so many YouTube tutorials nowadays for all instruments. Many of them are great and very well made! Anything you want to learn music theory-wise can be found on YouTube and, pretty much for all instruments, there are tutorials on how to play songs and scales etc..
I know several students who started off learning with such tutorials. They definitely learn the basics well. However, when it is someone learning with no prior music knowledge, there is the danger that they do not understand all concepts correctly and might misunderstand something or not learn it the right way. This is when live teacher feedback is most useful. Sometimes there is really no good alternative to getting correction and feedback from a teacher, either in a live lesson in person or online, or via sending them a video of yourself playing and asking for feedback on that.
The combination of online tutorials and live lessons can be very effective. I often encourage this with my students. The more different things they practice and learn in between lessons, the more they will develop and grow as musicians.