animation tab is shown on the window
need more information please, is this in Impress? what are you trying to achieve and how are you trying to do it? perhaps a screenshot will help.
In the sidebar, which is normally to the right of the window/screen, are some icons, one of which opens the Custom Animation deck. On the system I’m writing this on, it is a yellow star. There is also a set of 3 vertical dots at the top right of the sidebar which, if clicked on, give a menu which includes Custom Animation, click on that entry.
I hope this is what you’re looking for. Cheers, Al