Hello i dont know how to report this, don't know the section btw
This is my system
Intel i5 4670 with AMD Radeon 7870 with Asrock Fatal1ty H87
version 5.5.4 plasma
i have this problem with manjaro KDE but also on Kubuntu

Shortly, i have little freezes of the plasma workspace, i can move the mouse but the clicks does nothing, this for 3-4 seconds, than everything returns to work. It is continuos, but no crash or ifo reported
I dont know how to solve or exactly to report

Is everything affected or only the desktop itself (and panels)?
Does it go away when you suspend the compositor (SHIFT+Alt+F12)?

it seems all freezed and only the mouse cursor works, it moves but don't click on icons..
Pressing alt + ctrl + f12 it enters in like console mode...and stays in this mode no GUI back

SHIFT + Alt + F12 ....

Not a solution because, alt + ctrl + F12 takes me in a full konsole mode, and i cant go back, i have to reboot giving the command.

And the freezes isnt a single time, but many freezes costantly using the pc

Who told you to press CTRL+Alt+F12?

Login, then press SHIFT+Alt+F12 to suspend the compositor and see whether the freezes remain.
Again: *S*H*I*F*T* + Alt + F12 !