Whenever I try to change the default aggregation or theme on a specific folder to override the default, nothing happens. The folder refreshes exactly as it was. Going to the folder properties again, it shows the unchanged setting. No matter how many times this is done, it does not affect the message list.

STEPS TO REPRODUCE
1. Right click on a folder -> Folder properties
2. Go to the View tab. Change either the aggregation or theme by unchecking the relevant checkbox and selecting anything from the combobox.
3. Click OK.

OBSERVED RESULT

1. Folder refreshes as it was. No change performed.
2. Go back to Folder properties -> view
3. Settings are as their default; no changes were performed, despite changing settings and clicking OK.


EXPECTED RESULT

Changes to the default aggregation/theme of a folder should take place and be saved properly.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
Gentoo Linux - KDE Applications 20.12.2
KDE Plasma Version: 5.20.5
KDE Frameworks Version: 5.77.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION

This is happening on 5.16.2 (as reported by help -> about kontact) but the version selector here in the bugzilla does not have it as an available version.

It does not seem to matter how many messages are in a folder. Can reproduce this on a folder with 68 messages as well as one with over 130k messages.

Also this was a fresh installation after >1 year of not using Kontact/Kmail. No settings of any kind related to Kmail/Akonadi/similar packages were on this system.