What are some of the good conferences to go to that are related to mobile app development?

My knowledge is a bit dated.

• For Android, DroidCon is great, and it happens in many cities around the world. Of course, Google I/O is enormous and has a decent focus on Android content.
• For iOS, I found this list: https://swiftpublished.com/article/ios-swift-mobile-conference. WWDC is the Apple equivalent of I/O and I've heard good things about it.

Go in person

I was a speaker at the virtual Chicago Roboto in 2021: What You Didn’t Know About Retrofit with Kotlin. This was a great experience, but I highly recommend attending in person if possible. The connections and hallway conversations can be incredibly valuable.

Don't limit yourself to just mobile dev conferences

I'd also encourage you to go to conferences about the underlying or adjacent technologies, so KotlinConf or Deep Dish Swift. Also look into discussions on things like the build system, performance-focused conferences, or other areas you care about.