I'm not reproducing your problem. The samples worked on my system. With the video selected, the animation buttons were available.
Does it happen if you open PowerPoint in Safe mode?
https://support.office.com/en-us/article/Open-O...
Safe mode is not a way to regularly use PowerPoint, but it is a valuable diagnostic step. If your problem goes away when you use Safe mode, we can walk you through other steps that may help eliminate the problem. Please write back.
If it does not go away in Safe mode, first try Quick Repair (takes 5 - 10 mins) , if that doesn't help then try Online Repair (Takes more than 30 mins but less than 1 hour in general)
https://support.office.com/en-us/article/Repair...
See also https://support.office.com/en-us/article/error-...