I want to modify the text, but the following red font appears. What happened? How to eliminate it?

Maybe the document is in a modified state (I don't know if this is right). There is a small and inconspicuous column at the bottom of the editing window, some of which are gray, and one of them is "modify", which is gray at ordinary times. Double-clicking it will turn black. Do you think it is black now? If so, it is working. When you right-click the red word, you should be prompted to refuse or accept it.