Help! Arcade expression to sum all values per globalid in related table

[andrewtillinghast]

Hi, I have a hosted feature layer "CCG_Idea_Submission" on AGOL. The layer has a related child table called "CCG_IS_Reactions." They both have records added by Survey123 apps -- "CCG_IS_Reactions" has a field called Support that is populated with a "1" integer every time someone submits a simple survey in another app.

What I'd like to do is to calculate a field [Support] in the parent table with an Arcade expression that sums up the field per parent feature. I'd like this to occur whenever a new record is added to the child table, not just a one-time static calculation.

Can anyone suggest an expression to do so? Thank you!

[andrewtillinghast]

Starting to think that what I'm looking for might not be possible using an Arcade expression as a field calculation - because as I understand it this would be a one-time calculation rather than one that would run constantly/whenever new inputs are added.

I didn't give the final intent in my original post - which is to feed this data into an ExperienceBuilder app. Maybe I could accomplish what I'm trying to do as a pop-up expression in a related map and then have the widget pull from the pop-up...