@arran4 @voracread With some specific packages there are conflicts between different versions, so you can only have one at a time installed even if they have different slots. I think a few of the core KDE packages are like that. I know that I had to remove some parts of KDE 5 when I installed KDE 6 on my Gentoo system.
@418teapot @dwawlyn BTW strace has some built-in filtering, e.g. strace --trace=openat instead of grepping for openat. Might make it a little easier.