I haven’t, I use my phone as a medical device, so I haven’t taken the grapheneOS plunge yet as I’m not sure if the medical app would work. Yes, you’d have to wipe your phone to install GrapheneOS. For authenticator, if the app you used doesn’t allow exporting them, you have to disable 2 factor on all services and websites that use the authenticator 2 factor codes, switch to the new phone and new app, and re-enable on all services to get the new authenticate code. Pretty shitty, that some authenticator apps don’t give you a way to export (I don’t think the google app allows you to, correct?)