Works for me, I just dragged and dropped an image file onto Google Image Search in Firefox. Only difference is I’m using X11 instead of Wayland. So either it’s that or it’s something else on your system.
Operating System: Manjaro Linux
KDE Plasma Version: 5.27.8
KDE Frameworks Version: 5.110.0
Qt Version: 5.15.10
Kernel Version: 6.5.3-1-MANJARO (64-bit)
Graphics Platform: X11