Unable to Trigger Submit button state with variables

Hi,

I'm creating a slide where the learner has to select options from 4 drop-down lists. When the timeline starts, the Submit button is set to the Disabled state. Once they select any option in each of the lists, I want the Submit button to be enabled.

I've created 4 True/False variables for this purpose, with the initial setting to be False:

1) Dropdown 1

2) Dropdown 2

3) Dropdown 3

4) Dropdown 4

When the learner clicks each Dropdown field, the related variable changes to True. Once all 4 variables are True, I want the Submit button to become enabled. But for some reason, when I try this on the slide, the trigger isn't working for me.

Can someone assist me with this, please? Sharing the slide, in case it helps.