Hi I just found that if you try to add a app whilst using a mobile it goes to load the apps option page and then it disappears.
Go to apps page click add built in app or user app and all you get is a box staying " install new built in app" and a close button. On Android using Chrome
It shows up for me on my pixel 3xl, what phone are you using?
You can also, request desktop site and that will make the screen much smaller and show work as well if you have your don't size cranked up or your screen is too small.