I believe that I explained this in my first reply to this topic:
“On the Timeline of your animated layer, at the frame you want your first opacity keyframe, do right-click → Tweening → Add opacity keyframe.
That will make the first opacity keyframe at that frame.
Then, you can use the ‘+’ and ‘-’ buttons on the Animation Curves docker.”
but could not progress when it said “Much like how we animated opacity above, we need to add our first transformation keyframe. To do this, first make sure that you have your layer’s Transform Mask selected , and then click on the add keyframe button at the top of the docker.” because clicking on the add keyframe button would not do anything( Animating Transform Masks section).
Please use a new topic for a new problem in future. It makes things much neater and easier to follow.
Version 4.4.8 can’t animate a transform mask. You need to use the 5.0.0-beta2 that you can download from the links here, in the Download section near the bottom of the page: Second Beta for Krita 5.0 | Krita
Please read the warnings via the link to beta1 at the top of the page.
The screenshot you show is for adding an opacity keyframe to a Transform Mask in 4.4.8, which can’t be done because it doesn’t make sense.
If you use the 5.0.0-beta 2 then you’ll see this if you press the ‘+’ button on the top row of the Animation Curves docker when a Transform Mask is selected in the Layers docker or Timeline:
The orange frame marker can then be moved along the top to a different frame to create a second animation transform keyframe for the parameters.
This facility is in early stages of development and some aspects of it are confusing and difficult to manipulate.
I suggest that you limit yourself to Position and Rotation and remove any parameters that you’re not immediately working on by turning them off with the eye-visibilty icons.
The up-down and left-right arrow icons are very useful for range scaling.