Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
When animating a mask's opacity, you cannot find the keyframes in the dopesheet. Is in another place instead?
I've found this bug report but it's not clear if is there a solution or if it's even a bug.
While the bug is fixed (if it ever does), you can use a math node set to multiply to control the opacity of the mask. Animate the values from 1 (full opacity) to 0 (no opacity). Those keyframes will show up on the graph editor or the dopesheet.
Animating the values
Required, but never shown