Hi @asker1,
The “A in a square” toolbar item sounds like the new Block Editor toolbar to me.
The WordPress classic editor didn’t support such things as text-over-images as far as I recall and can find, it’s likely that there may have been plugins to add that functionality however, but the majority of these are no longer actively supported and as a result can be harder to find.
I would personally suggest that you try to use the Block Editor again, I don’t know the last time you tried it, but it’s come a long way in the last 15 major releases of WordPress, and would likely allow you to create the image you wish to have.
I understand it may not be perfect for your needs in other ways, but you may be able to use it purely to create the image block and then switch back to the classic editor for the rest of the editing – I’m unsure if that’ll work properly though, please try testing it on a new post/page rather than the current page you’re working on!