Hi @Pot !
I’ve answered you here in the announcement post.
This is one of the current limitations of the new system. We’ve made something that is general and can work on the majority of elements/properties, but there are a few very special elements in UI Toolkit that require a custom behaviour and we didn’t have time to get to this one. I’ve mentioned a workaround in that answer.
A proper solution would indeed be to have some form of observable collection, but this is a bigger than that didn’t fit in the 2023.2 release.
Hope this helps!