Copy>Paste from OneNote to Mac Mail app turns text into an image

I use OneNote for Windows on my iMac (have been doing so for many years). Recently, when I have tried to copy text from OneNote to the Mac Mail app, it will not paste over just the text. It packages all the text into an editable image (in a "box" similar to to how text is held in a typical OneNote page).

In Mac Mail I try both "Paste" and "Paste and Match Style" ... and I keep getting the OneNote "box" inserted into my email.

The copy>paste works fine if I use the Web version of my email (outlook.com) instead of the Mac Mail app.

Images are attached below. In first image you can see the box around the text and the down arrow that calls up Mac image editing tools. In the second image you can see what happens when I click the down arrow.

One of the more bizarre Apple bugs I have encountered. Any ideas?