Describe the bug
We have a bunch of issues on 20.09. They're fixed first on master, when appliceable, and then backported.

Versions in use

Versions on 20.09

• Qt 5.15.0 but different versions are used for different parts, causing trouble.
• Frameworks 5.73.0
• Plasma 5.18.5
• Applications 20.08.1

We need to consider the support of these versions during the period 20.09 is supported. Brief description regarding the issues of different combinations of versions #98657 (comment).

Note, however, I have no difficulties with the setup we have on master #101369.

Versions on master

• Qt 5.15.0 (and 5.15.1 with qt5: 5.15.0 -> 5.15.1 #102216)
• Frameworks 5.73.0
• Plasma 5.18.5
• Applications 20.08.2

Plasma release schedule

cc @doronbehar @ttuegel

Issues

• systemsettings5 partially broken systemsettings5 / KDE config broken with update to 20.09 #102253 .
• notification center is broken KDE Notification center is broken since NixOS 20.09 #102281 .
• wallet is not unlocked kwallet is not unlocked with SDDM #101904 .
• digikam is broken digikam is broken on release-20.09 #98879 .
• virtualbox is broken in combination with plasma virtualbox incompatible with plasma desktop on 20.09 #101023 .
• qt5.style is not working for mixed qt versions? adwaita-qt: dark theme for Qt applications doesn’t work on NixOS 20.09 #98009 (Fix: Move some qt5 style packages to qt5-packages.nix #102594 ).
• Can't set default browser (comment here).