If you don't need to work with the tables in question in ArcMap (though you do have ArcMap listed...), you could define Constraint Attribute Rules.
https://pro.arcgis.com/de/pro-app/latest/help/data/geodatabases/overview/an-overview-of-attribute-ru...
// Triggers: Insert, Update
// blocks the edit if the field NotNullable is empty
if(IsEmpty($feature.NotNullable)) {return False}
return True
// or in one line:
// return !IsEmpty($feature.NotNullable)
You won't be able to open these tables in ArcMap. You can open views containing the data, though. So if you don't do edits in ArcMap, this could be a solution...
Have a great day!
Johannes