You will need around 30GB of free space to use for this
Here is a quick rundown of how i setup Arch to build Plasma 6 and related KDE software. This will be relying on kde-unstable and arch-testing repos to ensure latest for everything, you should be aware of what that entails and be prepared for dragons.
You will need to know how to deal with build problems if you wish to do this, Im running with it installed to /usr (requires sudo) but default is not this. If you wish to do it the way i am youll need to figure that one out yourself as thats not the default nor recommended.
- Lets enable kde-unstable and arch testing, before proceeding PLEASE understand this isnt for someone who cant deal with at least a decent amount of issues on their own. You need to edit
/etc/pacman.confwithsudoedit. Near the bottom you should see entries like
#[core-testing]
#Include = /etc/pacman.d/mirrorlist
you need to remove the # from the beginning of each testing repo.
[core-testing]
Include = /etc/pacman.d/mirrorlist
After you need to add this to the beginning of the list just above [core-testing]
[kde-unstable]
Include = /etc/pacman.d/mirrorlist
- Once thats done here is the list of packages I installed for this, there may be duplicates/a few extras in the list as i just copied from my bash history and didnt check it too close
pacman -Syu python-pip python-pipx libraw dcraw power-profiles-daemon xdg-desktop-portal-gtk xsettingsd noto-fonts-emoji noto-fonts iio-sensor-proxy git cmake dialog poppler-qt6 qca-qt6 qt6-5compat qt6-base qt6-charts qt6-declarative qt6-multimedia qt6-multimedia-ffmpeg qt6-positioning qt6-tools qt6-translations qt6-wayland qt6-webchannel qt6-webengine qt6-websockets qt6-webview qtkeychain-qt6 qcoro-qt6 qt6-svg qt6-shadertools qt6-sensors colord libical python-psutil psutils python-sentry_sdk python-distro gdb libqalculate unzip libxrandr python-build python-installer qt5 qt6 appstream appstream-qt
- Follow the setting up dev environment Instructions to make sure you have everything and you setup kdesrc-build properly
https://community.kde.org/Get_Involved/development/Set_up_a_development_environment
- You can follow Directions as to how to build software here
https://community.kde.org/Get_Involved/development/Build_software_with_kdesrc-build
and more details here
https://community.kde.org/Get_Involved/development/More#Build_Qt_using_kdesrc-build
in order to build Plasma6/KF6 beta stuff you need to make sure to modify the kdesrc-buildrc. Change all the 5 to 6 and under the global options add
branch-group kf6-qt6
cmake-options -DCMAKE_BUILD_TYPE=RelWithDebInfo -DQT_MAJOR_VERSION=6 -DBUILD_WITH_QT6=ON
and according to the guide at the bottom add
options plasma-integration
cmake-options -DBUILD_WITH_QT6=ON -DBUILD_QT5=OFF
end options
options breeze
cmake-options -DBUILD_WITH_QT6=ON -DBUILD_QT5=OFF
end options
- Finally here is my kdesrc-build command i use based on the arch meta packages/plasma package group
kdesrc-build plasma-workspace plasma-framework plasma-integration bluedevil powerdevil plasma-nm plasma-pa plasma-thunderbolt plasma-vault plasma-firewall plasma-workspace-wallpapers kdeplasma-addons krunner milou kwin kscreen sddm-kcm plymouth-kcm breeze print-manager plasma-sdk kdeconnect-kde plasma-browser-integration xdg-desktop-portal-kde kde-gtk-config kgamma5 breeze-gtk drkonqi phonon flatpak-kcm kactivitymanagerd plasma-desktop systemsettings plasma-disks plasma-systemmonitor kinfocenter kmenuedit dolphin konsole kdsoap ksshaskpass kwayland-integration kate plasma-welcome baloo-widgets dolphin-plugins kdegraphics-thumbnailers ffmpegthumbs kdenetwork-filesharing kio-extras kio-admin xwaylandvideobridge kde-cli-tools kdecoration kpipewire ksystemstats kwallet-pam layer-shell-qt libkscreen polkit-kde-agent-1 --include-dependencies
if you get build errors you can resolve them and start from where you left off by adding this with the name of the item that failed to build at the end of the command
--resume-from "failed build item"
you can also resume after a specific item if you need to with
--resume-after "build item"
and if you need to rebuild things you can use --refresh-build
If you need to rebuild a specific item from the list with a patch added or changes you made without rebuilding all its dependencies you need to do
kdesrc-build "build item" --no-src --no-include-dependencies --refresh-build
This is a very basic setup that ive been using the past few days, If you notice anything strange here please let me know and i can make changes to this. If youre brave enough and feel confident you can resolve basic issues on your own and want to report issues for helping polish plasma 6 and friends I would say definitely jump on into building Plasma 6. 
how to run what you built is included here
https://community.kde.org/Get_Involved/development/Build_software_with_kdesrc-build
but thank you for the heads up