There is a mobile app for Android, but it is fairly simple; it is simply used for one-way publishing. https://discord.com/channels/698324796546482177/701232125831151697/809694808251433010
For most users, using Chrome on Android is the recommended way of connecting.
Not all cameras may appear as options when using a mobile device; this comes down to the manufacturer of the phone really.
If you cannot select your fish-eye camera, try instead buying a fisheye lens adapter from Amazon for a couple dollars; it will offer better performance probably anyways.
Screen sharing on mobile devices is not support via the Browser, although Android devices can screen sharing using the native Android app (linked previously). The screen sharing function may not include audio, or at least it might be unstable, and this will hopefully be addressed over time with additional development of the mobile app.
Android devices are not powerhouses; disabling video sharing for mobile users in group rooms if there are problems. More than around 7 guests in a room will probably require the Android users add &roombitrate=0 to their URL invite links, to disable their video sharing to other group members.
If using Android 11 and the camera selection page in OBS.Ninja freezes, push the browser to the background and then open it to the foreground again. This will unfreeze the window. This is a bug in Android 11; not OBS.Ninja.
USB audio devices should work with Android devices, but it will depend on numerous factors. In most cases, the 3.5mm headset port on some Android phones will be the most reliable way to attach an external headset or microphone.
On-screen overlay apps may cause some Android devices to get errors when trying to select their camera via the browser. Disable any apps on your device that may be causing an overlay on the screen or has the power to do so. Try the native Android app if this fails still.