Can anyone help me learn how to put images into submissions / "questions"?

I've been trying to do this for the past week and nothing seems to work.

I see three mechanisms offered:

Via the + button (image insert), which opens a window of recent downloads and option of "show all files" and selecting one by clicking on it.

Via the formatting and other options that show up if you highlight a block of text, which opens a drag-drop window, but the window is underneath the submission window and grayed.

Via ctrl-P, same drag-drop window.

Regardless of whether I drag-drop or select a file, what happens is that a grayed-out image appears in the submission window, usually with blue sizing lines around it. It almost always disappears if I click it or do pretty much anything. I gradually figured out that an "upload error" message was appearing, again, UNDER the submission window. But even in those instances that seemed to upload successfully the image would usually disappear. I did succeed once, I thought (don't remember how), but when I sent the submission with the images, the recipient got a message with blank squares where I had put the images.

I am probably overlooking something obvious, since everyone else seems to be able to do this, but I would really appreciate some guidance from anyone who can offer it.

(I would submit a ticket but from what I gather those don't get a response lately.)