Hi there and welcome
You need to open Pacifist, then within Pacifist open the Quark installer (just the package file) and it will then run the installation without the check of your OSX version, so bypassing this. But you do it within Pacifist
I can also do these steps for you, and have made a request via Additional Services. This is optional, and if you choose to do this, I can, with your permission, remote into your computer while you watch and do all these steps (and deal with any problems that arise during them) for you. Or if you do not choose to take this service, we can continue here. This is no problem at all. Just let me know please.
else let me know the results please.