Flatpak support is built in from MX 18 and later. It is only required to activate the Flathub repository following these instructions:
Open MX Package Installer (open the menu and look in MX Tools), select the "Flatpaks" tab, to activate the repository you will need to enter the root password.
I wakken ad yemmed usebded, ales asekker n unagraw-ik·im. Tura yegra-d kan ad tesbeddeḍ isnasen.!