Can you please provide more details on what fails when using strict confinement? As per the Process for reviewing classic confinement snaps a file-manager does not fit within one of the supported categories for classic confinement so it would be best to try and get system-g working with strict confinement. Please provide more details and we should hopefully be able to get it working under strict confinement (even if perhaps some use-cases are not able to be supported).