The default for blender 3.3 has the mask display unchecked for whatever reason. Located by the overlay menu.
By clicking on the dropdown you can turn on both the spline (which will then display the points you're attempting to create) and the overlay. I recommend using combined so that you can see your mask settings over your render.
I don't have much experience with the masking tool in video editing, but I found these two videos extremely important/helpful as I ran in to a couple other issues myself while setting up the mask for a video:
Applying the mask to your video edit: https://www.youtube.com/watch?v=wGjmNkjl5BM&ab_channel=MichaelChu
Explaining how to use masks (very generally): https://www.youtube.com/watch?v=ix8tmIdLRZg&ab_channel=BlenderFrenzy
Hopefully this helps in some way!