I get bunches of emails asking what happened to the "Custom Fields" meta box on the "Edit Posts" screen. They're hidden by default with the new Block Editor, so questions like, "do I need to install a plugin to get them back again?" No you don't. To view the Custom Fields for any post click the three dots in the upper-right corner of the screen, and then go to Options. There you will find a checkbox to enable Custom Fields (under "Advanced Panels"). Scroll down the page and you will see the Custom Fields meta box.