I still do it how I did it before, without the paper clip. First off, I use an old school digital camera and my file sizes are always too big, so I go to this site to reduce them:
https://www.reduceimages.com/
It doesn't do much but it does it well and doesn't set off my virus scanners. I resize and download the image there.
I use Firefox as a browser and my system is pretty locked down in terms of virus protections, I often don't see quite the same things screen shots show.
Then I start typing my message in the Quick Reply box. When done, I click on the Go Advanced button. The Manage Attachments does not stand out, it is in the middle of the options. I click on there and get to where I can download which for me is my downloads folder so that is easy. Then I have to resize the window, it still defaults to the old vertical layout and the new one is horizontal. The actual button you need to attach the thumbnail is to the far right.