Using Arcade is a good way to go. While they are not "real" fields they can do must things. Eventually Attribute expression may be more what you want but they are not here in AGOL yet (heard soon so look them up also). You can also go old school and run a nightly script.
You will want to look in to the Arcade FeatureSet functions. They allow you to look into the related records and grab info.
For Ops Dashboard take a look at Data Expressions. They combine Arcade expressions into new data.
Below is some sample code and check out these links.
https://community.esri.com/t5/arcgis-online-documents/using-featuresetby-functions-in-arcade-to-dril...
https://www.arcgis.com/home/group.html?id=ba3070ceede54f1981012811c51b7f78#overview
https://www.esri.com/arcgis-blog/products/ops-dashboard/announcements/introducing-data-expressions-i...
There was also a great post on this to calculate days past and such but I cannot find it.
Sample Ops data expression lookup
var p = 'https://arcgis.com/';
var tbl = FeatureSetByPortalItem(Portal(p),'d14444449',9,['UnknownCode'], geometry = false);
var dups = []
var Dict = {
'fields': [{ 'name': 'dups', 'type': 'esriFieldTypeString' }],
'geometryType': '',
'features': []};
var index = 0
var last = ''
for (var f in OrderBy(tbl, "UnknownCode")) {
if (f.UnknownCode == last) {
Dict.features[index] = {
'attributes': {
'dups': last,
}}
++index
}
last = f.UnknownCode
}
return FeatureSet(Text(Dict));
Hope that helps
