So far the answer is:

Some checks to vet the risk:
 * Has been updated in last few months (maintained)
 * Developer has resources to debug
 * Big Organisation where reputation loss is an issue
 * Reviews do not mention security issues
 * Doesn't ask for permissions it shouldn't need

If no to any of these, then don't use the app.

Project/developer has reviewers/Large, popular open source app across multiple platforms
 * This may be ok but I'm unsure if that works, as it depends if the code is reviewed.

Use ios
 * Need evidence that Apple does more checks and suitable ones compared to Google.  I think Apple has a higher reputation for Security on it's products, app store than Google, whether that is fair or not needs an answer...

https://www.howtogeek.com/224096/why-iphones-are-more-secure-than-android-phones/ - 2015

https://www.makeuseof.com/apple-vs-android-which-is-more-secure/ - 2022

Permissions
* I keep being asked for sensor access for no reason I can see on major apps on Google Play that wasn't there as far as I know for ios

You can block the odd permissions later?, ref GraphenOS
* Not sure this is viable for many users