Finally got it to work.
I added the working xorg.conf for nvidia prime as an attachment.
Maybe it will help someone else too.
Please tell me if you see anything in it that shouldn't be there.
Thanks to all who helped me with this.

-- 
Linux-gentoo-x86_64-Intel-R-_Core-TM-_i5-7400_CPU_@_3.00GHz

COMMON_FLAGS="-O3 -pipe -march=native -ftree-vectorize -ffast-math 
-funswitch-loops -fuse-linker-plugin -flto -fdevirtualize-at-ltrans 
-fno-plt -fno-semantic-interposition -fno-common -falign-functions=32 
-fgraphite-identity -floop-nest-optimize"

USE="-* git verify-sig rsync-verify man alsa X grub ssl ipv6 lto 
libressl olde-gentoo asm native-symlinks threads jit jumbo-build minimal 
strip system-man"

INSTALL_MASK="/etc/systemd /lib/systemd /usr/lib/systemd 
/usr/lib/modules-load.d /usr/lib/tmpfiles.d *tmpfiles* /var/lib/dbus 
/lib/udev /usr/share/icons /usr/share/applications 
/usr/share/gtk-3.0/emoji"