In Manjaro, I just had to switch to the stable branch, then run "sudo pacman -Syyu | grep "warning:". And then put all the warnings in a text file called downgrade.txt, and then run "cut -d ":" -f 2 downgrade.txt | tr -d '\n'", and then run sudo pacman -S copy and paste all the packages from the last command. That'll downgrade to the stable version, you probably will want to run "sudo pacman -Syyu" after it's done.
I was originally doing it manually, but got tired of doing it.
To lazy to figure out what package broke OpenGL. So I just went back to the stable branch.
If you are already using the stable branch, then you have a different problem.
The unstable branch gets updates, but doesn't update the dependencies, so you end up with a broken system.
Tried downgrading the packages I just updated to in the unstable branch, but that didn't work. Might of missed a package. To much work to manually downgrade. So I just switched back to the stable branch.