A few days ago, I decompiled and edited the Hyperspin APK to allow users to use 32-bit and 64-bit installations of Retroarch together. It's been confirmed working by the community and you can find that edited APK here: https://zerojay.com/nextcloud/index.php/s/3QfPqYM4A6ymjr4
It works as you would have originally expected using a 32-bit or 64-bit version of Retroarch to work, so in your Settings_Android system ini file, change the exe to com.retroarch to use the 32-bit version or change it to com.retroarch.aarch64 to use the 64-bit version.
Currently, both 32-bit and 64-bit versions of Retroarch will be called using the 32-bit configuration files, however I will likely be updating the APK to allow you to use the 64-bit configs as well for those who may wish to use different settings for both. When that happens, I'll keep both versions of the APK available so that you can decide what you want to use.
So now that the community has solved the Retroarch 32-bit problem, it would be really helpful to compile a list of cores and the version of Retroarch that it works best under. In some cases, certain cores currently only function under one or the other, but not both. In some rare cases, cores stopped working like Daphne, so again, these are things that we would like to call out. (By the way, for anything like Daphne where more recent cores no longer work, I can host them for the community if needed. Just let me know (and I do myself still need to get that working Daphne core myself).
I'll update the top post here to reflect the community's findings so that people only need to come to one place to find the info they need.
--- Core Information ----
atari800 - non-functional on 32-bit due to Android security changes, use 64-bit Retroarch core.
mame - Latest version of MAME core only recently started compiling on 32-bit, not available yet on 64-bit.
EDIT: Updated link for latest updated build.