How I mark fiction without ruining the flow

I used to avoid annotating fiction because it pulled me out of the scene.

Now I keep it simple:

1. Underline only lines I would want to quote later.
2. Put a tiny dot in the margin if the page has an idea worth returning to.
3. Write one sentence at chapter end if something changed my view.

No paragraph-long notes while reading.

Then after finishing the book, I flip through only the dotted pages and write a one-page note.

That keeps reading immersive and still gives me something useful later.