At pro 2.4 ESRI implemented attributes rules at the file Geodatabase Level which is great.
It means that when you copy or move the file geodatabase, you copy or move the rules.
So if you upload this fgdb to AGOL, the rules are uploaded within the fgbd.
Attribute rules are « able to travel » to AGOL.
At the moment these rules are not interpreted or implemented at the AGOL level.
The idea here is to have the rules interpreted and implemented in AGOL when publishing feature services from a rules enabled fgdb.
It would be great to have attributes rules fully implemented in ArcGIS Online.
This would allow users to have their own QC and field calculation in hosted feature layers and web apps !
(edited 2020-07-24 to improve this description)