Several ways to get photo into your post. One way to do it is to upload as part of post as you did. After you've clicked on upload, look for link under "Current attachments" below. Right-click it and pick "open in new window/tab" and your photo opens in new tab. Copy URL at top of that new window/tab and use it when asked URL when clicking on embed-picture icon. This is URL of your photo -->
https ://www.ninjette.org/forums/attachment.php? attachmentid=46317 &d=1570291031
Annoying thing is you get embedded picture in post as well as attachment preview below.