Hi @Aurora.MA,
Thanks for sharing this with us! It sounds like you're referring to the "auto-flow" feature in InDesign that automatically creates new pages and links text frames when placing a long text. By default, this doesn't happen when you just paste text into a text box - it only works when you place (File > Place) the text and then use Shift + click on the page. Holding Shift while clicking the loaded text cursor activates "auto-flow," allowing InDesign to automatically add pages and flow the text across them.
If this was working for you earlier with just copy-paste, it might be that the frames were already pre-threaded or master pages had threaded frames set up, which gave that impression.
I'd suggest trying File > Place, then holding Shift when you click - this should bring back the behavior you're looking for. Let me know if this helps or if you see anything different on your setup, along with your InDesign version and OS.
Looking forward to your update!