While it's working correctly in Konsole, I can't configure the translucency or enable a blurred background in Yakuake at all.
Instead under "Appearance" of the profile settings, I get a warning message instead of the configuration widgets:
"Konsole was started before desktop effects were enabled. You need to restart Konsole to see transparent background."
Does the blur appear if you reboot your machine?
See bug 395520.
Sorry Nate, should have added that: no, this warning message always appears, even after rebooting / starting a new session.
*** This bug has been marked as a duplicate of bug 395520 ***
From Bug 395520:
> 18.04+ has a call apps can make to determine if the profile has blur
> enabled. As I understand it, the app is responsible for enabling blur in
> its code (mainwindow), not konsole kpart.
Looks like Yakuake needs this done?