Well…I’ll make an attempt at this one…
View attachment 111267
Note the row of thumbnail images across the bottom. In the image furthest to the left I have clicked the area that had previously said “insert…”(as appears in the rest of the row). Now one is able to choose between posting the thumbnail or the full image.
These thumbnails appear at the bottom of the post as images are added, and the choice can be made, during the process of making the post…or when editing, after the fact.
I hope this helps.