Admob alternate

Other than admob, are there any ad sources to show ads mainly for Android app. Does Facebook audience network sdk available in gdevelop?

None natively integrated. You would need to learn the SDK you want to use and implement it via Javascript events.

You can try this Leading Reward Video Ad, Monetization Platform for Games | Rewarded Video Ads for Facebook, WebGL, iOS, Android App | Mobile Game Monetization
You need to code your own SDK but it’s simple
Here an example on one of my games
✅ Publish your HTML5 games ✅ | Game: A Pixel Adventure - Pairs

When you first load the page an Ad will appear, but it’s because was coded like to, you can even offer rewards. Take a look at the documentation as I said it’s pretty easy to integrate.

Other option is or in Game Distribution I have 1 game giving about 30€ for year
An old game made with Construct 2
Publish A Pixel Adventure Vol 2 on your website - GameDistribution
Hope this helps.