WhatsApp and my banking apps work fine on GrapheneOS (and /e/OS).

Which is why /e/ OS and Graphene OS adoption is higher than projects such as PostmarketOS (now Nura) or Ubuntu Touch, even if they are already quite mature. I daily drove Ubuntu Touch for two years in 2019 and 2020, and it's the need of Signal which made me switch to /e/.

Once upon a time WhatsApp had a j2me client…

Though I see signal usage creeping upwards. Maybe just my circle

Couldn’t the EU pass a law to require e/os/ to support WhatsApp or vice verse?

The problem doesn't lie with e/OS/, nor any other alternative. Google locks down capabilities with "Play Integrity", effectively attestation for official Google approved operating systems only. If you aren't on the list you fail the checks, and apps (like banking apps) will fail to run.

But it’s banking apps that opt into that. It’s not like Google is saying you must use Play Integrity. It’s a feature that banking apps are more likely to use. The EU could require banks to make apps for other operating systems.

IIRC EU was the issue?

"EU Age Verification Project Mandates Hardware-Bound Attestation"[1]

[1]: https://www.reddit.com/r/Android/comments/1vds3jm/eu_age_ver...

Someone should get the EU to ban the EU from requiring age verification.

No WhatsApp would be a feature

I wish we would all live in such a beautiful world; unluckily, the real world is not as nice.

Sailfish OS devices have good support for running Android apps.