You want kdesrc-build for that. Installing it is not really easy, there should be a package at least on KDE Neon repos.
KDE
KDE is an international technology team creating user-friendly free and open source software for desktop and portable computing. KDE’s software runs on GNU/Linux, BSD and other operating systems, including Windows.
Plasma 6 Bugs
If you encounter a bug, proceed to https://bugs.kde.org/, check whether it has been reported.
If it hasn't, report it yourself.
PLEASE THINK CAREFULLY BEFORE POSTING HERE.
Developers do not look for reports on social media, so they will not see it and all it does is clutter up the feed.
Thanks, I may try it sometime. I have a Neon installation in one of my partitions already.
Using Gentoo might work if you enable the KDE overlay: https://wiki.gentoo.org/wiki/KDE/Ebuild_repository
Gentoo supports slots; which allows for concurrent installations of things like desktop environments. Not sure if it's configured that way right now though.
If you use BTRFS you could install gentoo on a subvolume and boot into it when needed too.
@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.
I've only recently moved back but I was using it before the KDE4 release and you could do it with 3.x. Shame