I just created a post with the block editor where I discovered that you can switch over to the classic editor without using the classic editor plugin. I was able to create a tiled gallery using a plugin that the block editor did not support. The only thing is that the interface is so confusing that I don’t remember how I accessed the classic editor. I could really see how this will confuse people.
I also created another post with the block editor where I embedded the url of a You Tube video. It worked but when I published the post to view it, it showed the video below a large blank space below my last line of text. It appears fine in the editor window.
Update: I found how to enable the classic editor by clicking the plus sign + –>Formatting –> Classic
When I added a plugin, I got an error message that said “504 Bad Gateway” when I returned to the plugin directory. I returned to normal after I refreshed the page.