I use hidden networks and frequently have to return devices I purchase on Amazon because they can't imagine connecting to something that doesn't appear on a Wi-Fi scan. So not supporting hidden networks certainly has precedent.

However the antennas in many of these M5Stack devices are not great. Their Wi-Fi scans miss a ton of nearby networks, so perhaps it would still be helpful, even for normals, to be able to type in an SSID to connect to.