In todays piano teaching methodology the ability to sight-read is not among the first skills one has to acquire. Sight-reading is already a very complex thing and when you sight-read it means that while sight-reading you have to simultaneously play the piano too. So it expects the ability to play the piano plus the ability to sight-read.
These two together are a huge task for anyone. Therefore it is not good to start everything at the same time. It is way easier to learn when it is possible to concentrate on one thing at a time, then master it and take a next task for learning.
Because of these reasons a pre-sight-reading period is usually what helps and adult beginner pianist to get good piano playing skills. Then you can solely concentrate on building a strong basis for you piano technique and playing abilities. When you feel confident about your basic piano playing skills, it is possible to learn sight-reading much more efficiently. So being not able to sight-read is not an obstacle to start with the piano course.
If you are able to sight-read and you join the free online piano course – it will not disturb you at all because in the course for adult beginners, building up your efficient piano technique is the first thing to do and it is done without a need to sight-read.
Hope it reinforced your confidence and gave some insight.
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