Well, YaST only knows about and shows packages that are in one of your configured repositories.
If you want to install packages not part of the distribution, you’d need to add a repo containing them first for them to show up in YaST.
Those 1-click installs at software.opensuse.org automate that process though.
Is there another way to get rid of the splash screens in booting up and shutting down?
Sure.
Uninstall plymouth, or add “plymouth.enabled=0” to the kernel boot options.
I like that option. It seems the simplest. I have looked in several places in YAST (Kernel Settings, Boot Loader, and /etc/sysconfig Editor) but can find a place to make this change.
Go into YaST->Boot Loader and switch to the “Kernel Parameter” tab, you should see a text field labelled “Optional Kernel Boot Parameter” (or similar).
Btw, I noticed I made a small typing mistake, it should be “plymouth.enable=0”…