With SwiftUI and Jetpack Compose on the horizon for iOS and Android developers, respectively, you should really invest time into learning those frameworks.
A whole lot of those problems are C++ related and a consequence of starting this very early and possibly going too far. A lot of companies have had good success with code sharing.
https://news.ycombinator.com/item?id=20695806 "The not so hidden cost of sharing code between iOS and Android" (dropbox.com)