Since this thread is also getting some reaction (likes and whatnot), I wanted to tack a link to the Github Repos for OpenCV-C and Xojo-OpenCV-C onto it, for posterity.
You can read a bit more about the project in this announcement post
The OpenCV-C Repo is here. This provides a plain C wrapper for most of OpenCV 4.5.
And the Xojo-OpenCVC Repo is here. This is a Xojo project that incorporates OpenCV-C as a set of classes that handle the nuts and bolts stuff like creating and destroying mats, etc.