How to fix Yakuake window placement in KDE Wayland:
Step 1:
Set up a window rule for org.kde.yakuake and add the property "Initial placement" and set the value to "Force" and "In Top-Left Corner" Like in this pic:
Step 2.
Change the width of yakuake to take up the entire width of your screen.
Step 3:
???
Step 4:
Profit!