“Istadh, there are acts of worship that I have stopped doing because I feel that my heart is not doing them purely for Allah, but for other reasons such as reading the Qur’an, seeking knowledge, or wearing the hijab. How can I become sincere in my acts of worship

This is a common case that the shaitan tricks you into. You are doing all of this for the sake of Allah. It is just that the shaitan, when he sees the worshiper turning to Allah Subhanahu wa Ta'ala, starts giving them these thoughts. They start saying, "I don't feel it," and so on, just because there is some hardship in it. Everything in life has hardship. However, we are doing it for the sake of Allah, and we need to continue until it becomes a natural behavior for us—until it becomes part of our identity. Insha'Allah, you have to be patient and persevere until you reach this level with time. This needs years.