I need to indicate my users that certain action is not possible, but hidding button is not the right UX. Instead, having button disabled that does’trigger the action is the way to go.
How to achieve this in Glide? Probably custom CSS? Anyone has done this?
Inside the custom action add an else branch with a show notification.
Another approach
If you want to also change the look and/ or icon have two buttons on the screen with opposite visibility settings.
That’s good but still don’t know how button to look disabled without CSS?
To prevent the button from disappearing, you can simply add a notification when the conditions are not met in your custom action.
To disable your button follow the following link: Exploring the Enhanced Capabilities of Glide’s Native Form
What I normally do when I put two buttons on the screen with opposite visibility
One button with accent color on and appropriate icon and the other button with accent color off and a lock 
icon.
I use hint component with opposite visibility to button. Rather than playing with css