Just don't want any conflicts. Also, are there more endings to choose from in 2021 version than 2008?
Thanks
It’s hard to remember 2008. Did that have the four-bar ending? I’m pretty sure that is newer. For one thing, RealDrums only began in 2007 and RealTracks in 2008. You will find a world of improvements.
Remember Ctrl+T. It will help you feel more at home using the older interface.
Usually you should install on top of older versions. This is to ensure you keep your songs, user styles, and bonus pak purchases.
I'm pretty sure that 4 bar endings were added because of RealTracks. BiaB 2008 had very few RealTracks and I'm also not sure about the availability of endings. However, the choices of so many new Styles would certainly give you more flexibility.
As advised, installing directly over the top of your existing installation is the recommended method.