FYI, I just tried using Compose key in Konsole, and it works for me.
The way it's set for me is:
System Settings > Keyboard > Key Bindings >
Position of Compose Key > Menu
That makes my right Compose key (which KDE treats as Menu key)
work correctly.
Doing something like Compose + o + o produces a degree sign:
°
I'm also using Wayland session, konsole 24.08.0, Plasma 6.x.
Regards,
Shmerl.