The default RTF reader on a Mac does not seem to support embedded images and most of the other apps don't seem to have an eval available or they require newer versions of the MacOS than High Sierra to be able to install it. And those that will install require that you purchase to try and don't say if they support embedded images or not. I tried LibreOffice's free trial, and while it supported embedded images, it did not do it very well (had white lines throughout the images).
So, I compiled your sample using Delphi 10.4.2 and installed in on my very very old MacBook pro which is maxed out with High Sierra 10.13.6 with Xcode 9.4.1, and it seems to work just fine with embedded images (I didn't do much testing other than that)
I was wondering if you thought about posting that compiled app into the Apple Store (preferably as freeware). If you don't think you would want to do that, I might dumb the demo down a bit for my specific usage and try doing that myself (don't know what's involved in publishing to the Apple Store). Why do I need something like that? Well, we provide an RTF Report Summary of a home inspection that realtors can edit for their clients, but some realtors use Macs and don't have Word on it, so it displays garbage for the embedded images. If they can get a free and simple RTF editor that supports embedded images, it would be great.
What do you think? :)