Huh? I'm running kde plasma on wayland and flameshot runs like a dream come true. I hit the flameshot icon in the tray, it automatically selects the whole screen to save, or if I click it starts cropping wherever I move the mouse. It's like the devs read my mind for exactly what I wanted

Every Wayland compositor has a different feature set, and KDE is one of the more open to implementing features. It's likely that other people have compositors that stubbornly refuse to implement screenshots for security reasons.