Learning to play classical piano can be quite different to how you learn to play modern piano or jazz piano, because there are obviously significant differences between the three genres.
If you want to play classical piano, then you will need to learn to read music. With the other genres, it isn’t quite as necessary to learn to read music, but with classical music, it is essential. There are some content creators on YouTube that will have the odd video where they teach you to play a really well known tune and the version that they teach you is simplified so it is easier to play. There is nothing wrong with this, but if you want to be able to play classical music, then you probably wouldn’t be satisfied with this and you would much rather play the original.
To be honest, I think that the vast majority of people that want to learn to play the piano in retirement would be happy playing the modern, popular tunes. This does not mean that there is not ones who really want to learn classical music. If classical music is what you want to play, then do not be dissuaded.
For learning to play classical piano, I would recommend getting a piano teacher that teaches classical music. This would be the ideal way to go because they can lead you in the right direction, teach you the skills that you need and teach you to read musical notation. If this is not possible, then I would recommend that you search YouTube. While it seems that most of the ‘how to play the piano’ videos are aimed at the modern popular genre, there is still some material for those that want to learn classical music.
If scrolling through YouTube videos is not for you, then I would recommend getting a piano tutor book, that is the first of a series of piano tutors, so that you have a definite path you can follow. There are adult piano courses available and there is nothing wrong with them at all, but I would not recommend them if you were going it alone without any help or input or feedback from someone who already plays the piano.
What I would recommend is a piano course aimed for young children. The reason why I would make this recommendation is that piano books aimed at the very young, takes all the knowledge and information and presents it literally one step at a time. These books teaches you one concept, then gives you a few pieces to practice and learn before moving onto the next concept. Comparing this to piano courses that are marketed to adults – these tend to introduce several concepts at a time and sometimes I think they move way too fast.
I realize that these piano courses for young children have quite infantile pictures to make the book more visually appealing for their target audience, but mature adults can learn to ignore these things and focus on the quality, slow paced presentation of quality information.
While I have presented here what I think after a few decades of piano teaching, there might be others that give you a different approach. If you get conflicting information, then consider which source you think is more reliable and which approach would you rather take.