The accepted answer to the second question you linked discusses the reason this happens: the size limit is on the entire prerendered target Activity, not just the transitioned element(s). Adding android:transitionGroup="true" to the appropriate place in the transitioned layout will fix the crash. You didn’t post your layout in the question so it’s hard to know where that would go, but if you have a ScrollView or other very long view that would be a good place to start.
For API levels before 21, this is a non-issue. AppCompat.startActivity() will work on API levels below 21, but the shared element transition animation will not run. It will fall back to the default activity transition.