Minimum Android Version
Previously the minimum Android supported version was Android 6, and I've been using an early beta version of the zotero app on an Android 8 e-reader for over a year (slow but worked). But I just updated to the latest version and now it won't open any more. I was wondering if there were any changes to make it incompatible with earlier versions? The device in question is an Moann Inkpalm5 which only has 1GB RAM.
Also, can I only get apks from the Google play store?
Also, can I only get apks from the Google play store?
Upgrade Storage
Where you getting APKs from some other place before? There may be a change that those other Android build providers you've used has a version that is missing some components.
First what is the latest version you've updated to? Did you get it from Google Play Store?
Try installing Google Play Version.
If that doesn't work and app just simply crashes the moment you open it you will not be able to provide crash reports for us. In this case, you might try installing Android Studio, connecting your phone to it and look through logs for a red crash message and give it to us.
But really, it would be very convenient if you considered providing pre-built APK files on https://github.com/zotero/zotero-android - then we have an alternative way to get it and can use https://github.com/ImranR98/Obtainium for automatic updates, without you worrying about e.g, F-Droid builds.