No, models that are built new, or opened and saved in ArcGIS Pro, cannot be used directly in ArcMap. However, you can save the containing toolbox as a previous version and use that toolbox in ArcMap. It’s safest to make a backup of the original toolbox before modifying any models in ArcGIS Pro. Keep in mind that many tools and new data formats are only available in ArcGIS Pro, so the model still may not work in ArcMap.