I think its time and practice as others have said but also limiting your social media content consumption. After 2 months of limited app usage I have less im thinking about other than what is in front of me. It has also helped with my short term memory which was trash before and so frustrating to do RC.

I had the same problem and its likely because your attention is used to jumping around, thinking of something else while doing anything. Its really common to be like that now. I notice it when reading books the most. I had to make big changes like not listening to anything or looking at my phone while working, reducing multitasking. Limiting my utube watching to 1 hr total on the weekend. Deleting social media apps from my phone and having to re-download to check once a week. Deleting reddit. For me its not one solution just while I'm studying. Its a gradual process of training my brain to calm down and focus. Locking in is incredibly hard if you have scattered your attention for years. I wish someone told me that earlier.