The flag -y refreshes the package list (like apt update). For some reason, you use the flag -yy to force it to clear the whole package list and redownload everything.

To allow package downgrades when upgrading you use -uu.

These are very commonly suggested fixes to arch package management problems, for example when you leave your arch install to suit for too long, it will be impossible to update it because of dependency problems. So you google it and people are saying to run “pacman -SSyyuu” or other such commands.

Those additional options should be their own flags, command line flags should be idempotent (it should flip a switch on, doing it multiple times shouldn’t change anything).

Pacman flags not being idempotent (-SS, yy, uu and such existing) is so unbelievably horrible that I can’t use arch just because of it.