It seems to work the way that you want.
I’m not sure what the final thing will look like. I have to post before I can see that. And I think this goes into moderation, so I also have to wait until it is approved.
I did this the way that you wanted.
I started a reply by clicking “Reply” at the end of your message.
Then I selected a block of text. But I did not click the “QUOTE” button provided.
I then entered the quote block start and end in places where I wanted them. And it showed up as a quote (actually two quotes separated by my own text).