If you run an MSIX file of an already installed package, the only available button is the "Launch" button.
In MSI world, running an .MSI file of an already installed setup provides options for repairing and uninstalling. I would expect the same set of options to be available in the MSIX app installer, possibly in a dropdown menu in the right bottom corner (three dots or a gear icon). This would make some quick MSIX tests faster (no need to dig through Start menu or Programs section if you are just playing with a particular MSIX file) and - as outlined before - it would make it a bit more consistent with the Windows Installer behavior.