At the moment, the Mendix Native builder only supports .png files for the Splash Screen. Two of our customers already asked for animated splash screens (more than once).
Adding this functionality would greatly improve the look & feel of our Apps, especially because the start-up can be slow.
Any other people who would like to have this feature? I saw the question being asked on the forum already: https://forum.mendix.com/link/questions/102368