Hello Francisco, hello Albert,
this might be the same as in bug #996726
and not directly related to the nvidia driver.
I hit a crash in kwin_x11 with an AMD graphics card
and could workaround by installing
libkdecorations2-5v5_5.21.5-2_amd64.deb like
mentioned in #996726.
Kind regards,
Bernhard
https://bugs.debian.org/996726