Virtual Layers / Triggers and rendering

[meyerlor]

I'm struggeling a bit with the configuration of my layers. I have set up a nice project for QField (cloud) to collect tree data. The styling of the trees (points) is dependend on a field of their children (color coding of the trees should be by the maximum priority of their "ToDo" jobs. I solved this with a virtual field in the trees layer relation_aggregate('Bäume_Maßnahmen','max',"Priorität). In QField everything works fine, but in QGIS the map rendering with ~2000trees and ~1500 ToDo's is very slow. Is it possible to configure QGIS in the way QField works and not trigger the virtual field calculation everytime the map is moved? (I assume this is how QField does it?).
I have two more ideas:

• Working with SQL triggers in the Geopackage (will this work in QField "live" or just after uploading it into the cloud?)
• Using QGIS Actions (fire an update in the parent layer field whenever a child feature is changed)

Anyone tried one of those yet? Or got other ideas? :)