I don't really understand where's the issue: Kwin, Xorg or something about Neon, but when i start KDE Neon, all the desktop effects don't work, for example the Woobly Windows or shadows. Changin' from OpenGL 3.1 to OpenGL 2 or XRender solves the issue, then i put back Open GL 3.1 and still works fine. I have to do this every time i startup KDE Neon LTS so it's kinda annoyin'. since 5.12.
Sounds like a Neon issue.
LOL, apparently i'm an idiot. On compositor settings i had to set "use compositor at startup", i never saw that but still: why the option was set off updatin' KDE? Nevermind...