Yes. Map Viewer in ArcGIS Online supports adding, editing, and deleting related records.
If you created a relationship class in the geodatabase in ArcGIS Pro before publishing a hosted feature layer, and if the hosted feature layer was created using a template that includes a relationship class, or the hosted feature layer was created for a form containing a repeated section in ArcGIS Survey123 Connect, you can add related records to the form.
When you create a form in Map Viewer, you specify what elements the form contains and how they appear. Now, we have added a new form element for related records. When you’re creating a form for a layer that has one or more related tables*, you will now see a new form element for related records under ‘Form elements’. To add the element to the form, you can either drag and drop or simply click ‘Add all’. With this simple action, editors will now be able to edit features in the layer and the records in the related table.
Map Viewer supports editing related records that meet the following criteria:
Other things to note: