Unable to add models created in ModelBuilder to the Quick Access Toolbar in ArcGIS Pro versions 3.5.X and 3.6.

Solución alternativa

Add the model to any existing ribbon tab, or create a new ribbon tab and then add it to the Quick Access Toolbar:

1. Right-click the ribbon and select 'Customize the Ribbon'.
2. Select any existing ribbon tab, or create a new ribbon tab.
3. In the 'Choose commands from' drop-down list, select All Geoprocessing Tools.
4. Search for the model.
5. Select it and click Add. 
6. Click OK.
7. Open the ribbon tab that has the model added to it.
8. Right-click the model on the ribbon and select 'Add to Quick Access Toolbar'.
9. The model is added to the Quick Access Toolbar.

The model remains in the Quick Access Toolbar even after removing it from the ribbon tab.

Pasos para reproducir