When I edit the code or document, the cursor becomes a flashing block.

when you hit the code, accidentally you will encounter this situation:

  

The workaround is to press the INSERT key to resolve the INS (insert abbreviation) key on the notebook.

according to the encyclopedia, this is the case:

The Insert key (insert key, abbreviated INS) is a key on the computer keyboard that is used primarily for switching text input patterns in a word processor. One is overlay mode, the new input word of the cursor position replaces the original word, the other is insert mode, the newly entered word is inserted into the cursor position, and the original word moves back. In an earlier computer terminal, if in overwrite mode, the cursor would become a block instead of the usual vertical line.