Hi,
The command is update-grub.
You could once simple reinstall networkmanager with pacman -S networkmanager-qt5 when you want to force overwrite the previous files, use pacman -S pckgname -- overwrite "*" as option during install.
You can also remove first plasma-nm, then networkmanager-qt5, because plasma-nm package is the icon for network, what you get at your taskbar, then install both again.
If it still doesnt work, you may boot from your usb stick, then fdisk -l, cd /, umount /dev/sdx, fsck /dev/sdx the partition, where your system is installed.
Then reboot again into the usb stick, and chroot into your system, then you should have network too.
In case you dont know how to chroot, you can find some infos with a search.
Ie. like this
Then remove and reinstall the kernel again.
All that problems with ldconfig are broken packages, the easiest way would be to reinstall the depending packages. That was, what i did by finding them first with pacman -Qqkk or pacman -Qkk,
The packages what are listed with the first command can have problems, but it shows also packages,
where only files been changed afterwards, like settings files, configuration files etc.
So means, they are not all broken, but by reinstalling them it should fix the dynamic links.