If you do click on "Get" you will be installing the Google Photos app. Then it
continues by asking for permission to access all your photos (that's what the Google Photos app is for) and for you to turn on the Backup feature. If you do that, it will start backing up all the photos on your iPhone to your Google account. This may fill up your Google storage space.
Unfortunately, I see no way to make
the "Get" prompt go away. You just have to ignore it and scroll thru the photo album anyway.
Now, there's nothing wrong with installing Google Photos app if that's what you want to do. But you don't have to if all you want is to view a shared photo album.
If you use a computer to view a shared photo album, none of this happens.