My experience is mostly limited to iOS where adding a trusted root CA is relatively easy. It's uncommon for the average app, but most of the big ones do it. iOS

My experience is mostly limited to iOS where adding a trusted root CA is relatively easy. It's uncommon for the average app, but most of the big ones do it. iOS itself cert pins most things as well. But on Android, since adding a new CA is much harder, I'd guess fewer apps do it there.