What you are seeing is flow — the state where your child feels their best and is fully engaged. Your child is deep in a book and needs to transition to required work. The resistance you feel about interrupting is appropriate. Reading for pleasure builds vocabulary, comprehension, empathy, and sustained attention in ways that almost nothing else does. The required work is also real. The skill being built here is not compliance. It is the child growing ability to hold both things: their love of reading and their responsibility to other tasks. That skill starts with how you handle this transition.
I can see you are really in it. Find a good stopping spot and then we have some work to do.