GRUB - Qubes alongside other Linux


I have other Linux operation system which I want to use + the GRUB from that installation
I want to keep MX GRUB, and be able to load QUBES which Is installed on dedicated partition

before installation

After installation

I used ‘automatic’ installation, and choose which partition I want to preserve, and on which one system supposed to be installed.

Before automatic installation happened, I used custom installation option, but without success. Message that I saw was following.

You have not defined a root partition (/), which is required for installation of Qubes OS to continue.
You have not created a bootable partition

|How to install Qubes, so MX is installed, Grub from MX is installed, and I have option to choose between MX and Qubes?

Many Thanks