Floating text boxes, images, and tables get put into a different document "layer" in Word. That layer is reachable with the JAWS screen reader, but the user needs to switch between it and the main text of the document. JAWS is rather expensive, and many people use NVDA on Windows and VoiceOver on Mac, which have more difficulty navigating this layer. Additionally, the order of content will not necessarily be in the intended order, even if you place the anchors for the floating objects in appropriate places. This is why the MS Accessibility Assistant will call out floating objects.

If you are going to have a "layout" style document with floating images or text — a digital flyer, infographic or the like — your best bet is to export to PDF, then remediate it in something like Adobe Acrobat Pro, which allows you to set a reading order for content, and tag different elements appropriately.

So the answer is, you can do it, but you'll need more than just Word to make it happen.