Update for anyone wondering or encountering this issue in the future, I’ve found the case where it does not work for me:
As soon as some layer outside the Dropdown is a ListView, it does not work anymore.
I tried with 3 Data Views nested in each other, with the CustomDropdown placed in the most inner one, that works fine for me.
As soon as I change one of them to a List View, the Dropdown ID and Label are not set anymore for Microflows triggered by a Select Option.
Unfortunately, this makes it difficult (impossible?) to use a dynamic amount of CustomDropdowns.
EDIT: It seems to specifically be List Views. With Data Grids it seems to work fine.
Update on the Edit: By changing the List View setting to “Editable” under “General”, the issue is resolved and the CustomDropdown works perfectly fine.