There is a mobile app for Android, but it is fairly simple; it is simply used for one-way publishing. It does support screen-sharing though, so it has its value.
Download the Android APK file here: https://drive.google.com/file/d/1M0kv5nWLtcfl2JOnsAGiG1zUmkeIVLyZ/view?usp=sharing
If you have a UVC-connect camera, screen sharing the output of that device is also one way to bring it into VDO.Ninja. UVC-based devices are not supported currently otherwise via Android.
For most users, using Chrome on Android is the recommended way of connecting. There are some exceptions, such as for Samsung users. Using the Samsung Galaxy browser is recommended instead of Chrome for Samsung devices. On the Galaxy S21 for example, it seems that you can get 60-fps when using the Galaxy browser, but only 30-fps when using Chrome. If battery life or heat is an issue on Samsung or other Android devices, limiting the frame rate to 30-fps and possibly the resolution to 720p can allow the H264 hardware encoder to work (&codec=h264). The default target frame rate of 60-fps may prevent H264 from working on some phones, causing heat issues due to software-encoding being used. Firefox on Android seems to fix a couple Chrome-specific issues. Chrome will mute the microphone after a minute if the screen is turned off, but Firefox doesn't seem to do that. With Samsung devices, Chrome combined with H264 hardware encoding may have color issues with the OBS Browser source, but that issue isn't present when using Firefox as the mobile browser. So, for Samsung devices, you might find Firefox, with &fps=30 and &codec=h264 as parameters (push and view side respectively), may help keep things cool. 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. The Android APK version of VDO.Ninja will reveal a few extra cameras (wide angle, for example), versus the browser, but it doesn't support group rooms at the moment.
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.
Pixel devices have problems in Portrait mode, where the video may glitch to be all green or such at times. Using &codec=vp9 on the viewer side or &scale=20 can offer some solutions, maybe though. Try starting the device in landscape mode, then move to portrait, also to see if that helps.
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.