With the Classic Editor installed, you can switch between the Block Editor and the Classic Editor. It’s easy to choose which one from the list of posts, but how do you switch while editing the post or on adding a new post or page?
If you’re starting in the block editor and want to switch to classic editor, go to the upper right hand corner of your screen to the three dots and select Switch to Classic Editor.
If you would like to switch back to the block editor from the classic editor there is an editor section on the right hand side that says Switch to Block Editor.