SOLUSfiddler
the first, the first link, is the version to be copied by hand, which can then only be controlled via the terminal.
the second link basically contains the first version. but with an installation script and a gui.
first i installed the first version, which works without problems.
then i found the improved version, which comes with an install script and a gui. I had installed the gui from it.
I don't know whether this also works under plasma, which uses sddm as login manager. because the folder lightdm is in the path of the files to be installed.
in any case, i can switch between the intel and nvidia gpu. without reboot, just with out and log in.
you have the full unchecked nvidia power.
maybe the core team of solus should consider implementing this.
to maintain or to keep this up to date, IMHO is not an act. because there are probably very few updates.
for better understanding, you should read both.
I can only report on my experience with the simple variant. and that works great.
here are the links and a screenshot.
https://github.com/xulongwu4/nvidia-optimus-manager
https://github.com/Ronan-Kelley/nvidia-optimus-manager-gui