To be fair, people might have a genuine need to use this app, even if they don't want to be stuck inside Twilio's grasp.
I wanted to move to a different provider ages ago, but laziness made me postpone it until I had to do it today to avoid account lockouts.
After having done that. I experimented with downloading previous versions of Authy by using Aurora Store – the idea being that if they worked, they could be verified as legitimate packages using AppVerifier from Accrescent to compare them against the version installed from Play Store. Unfortunately none of the previous versions that could be downloaded was able to proceed any further. So my (uneducated) guess is that checks are being done server side, and not simply in the app.
I imagine using a rooted phone would also trigger their integrity checks – although it's probably possible to bypass that somehow, I don't know. It doesn't seem like a practical (or secure) approach for most users to do.
Unless Twilio listens to us and implements attestation for GrapheneOS, for people who are now locked out of their accounts I can't see another viable approach than to either borrow someone's else's phone or flash back to stock OS, re-register the MFA codes for all your accounts to a more reliable provider (Ente has publicly praised GrapheneOS) or one that just supports offline backups. Unless your employer mandates that you use this app. Then I guess you'll have to flash back to stock and keep using it while you wait for Twilio you reply, or get a second phone.
Do their desktop apps still function? Or is that also a dead end here?
This is just silly. Shaking my head as to why I didn't predict this would happen.
Edit: had to get past their birdbrained AI chat bot (apologies to any Twilio employee who might take offense) and found out that I needed to authenticate with MFA using a different phone number than the primary one registered to my account, in order to chat with a human. I don't think they have email? I have written a text that I will send them when I can sign in again.