my module dialogs are not appearing in GRASS 78 (for 76 it is working) e.g. I want to change the colour of a vectorlayer and click on the properties button, but no module dialog will open.
Under Windows, QGIS 3.10 is not compatible with Grass 7.8.0-2, QGIS only works with Grass 7.6.1. The solution is to use the OSGeo4W installer to downgrade to Grass 7.6.1 (I presume you are on Windows, like me). Runs the OSGeo4W installer again and click the Grass 7.8.0-2, changing it to 7.6.1-1. This will install the older version of Grass. These breaks in compatibility between QGIS and Grass have happened many times before.