Both of my banking apps work fine with a rooted GrapheneOS phone. If you want to have full control over your phone like you would a Linux laptop, to customize it to your own preferences and maximize privacy, there is nothing else gives you the same amount of control over the device that you bought and paid for.
The fact that people pay $1000 for a device and then not be able to fully uninstall pre-installed crapware nor fully block it from the internet is depressing.
The secret looks something like this:
JBSW Y3DPF QQHO ....
(usually fairly short unless its google)
Then you can import them into Aegis or some other FLOSS solution: https://github.com/uiltondutra/authy-migrate
Moreover, most of root tools and ROMs are rather poorly written and glued together with other forum scripts which you have no way of checking if they're not malware. (There are exceptions.)
So no, "safe" it's not and never has been. The tradeoff might be worth it for you as a user though.
> The reason I'm asking is that I'm stuck with authy as a MFA code app, and would like to move to something that has both desktop and phone support, and my conclusion is I'd need to root my phone to get access to the actual MFA seeds (they don't allow exports to keep you stuck in their app).
The way to do that is to take the hit and recreate your 2FA codes in an opensource app like Aegis or Stratum.
Personally I reject with extreme prejudice the android security model (it's my &#^@ device not the vendor's). But I don't generally want to grant any apps root. Lineage strikes a nice balance by providing root adb.