otpauth VS KeePassium

will generate a PNG file for each account, name after the account name and site name, and containing the QR code for the account.

Going forward, save those PNGs somewhere secure (I use an encrypted tar file). Any new accounts you set up save the QR codes for those as PNGs and add them to your collection. If you keep that collection up to date you will be able to readily handle any device updates or replacements readily or adding new TOTP apps.

[1] https://github.com/dim13/otpauth

afterwards you can use https://github.com/dim13/otpauth to convert the GAUTH code to plaintext

Open google authenticator, export accounts, screenshot QR code, decode with cyberchef, decode otpauth-migration link with https://github.com/dim13/otpauth

Scan the code with something else and pass the string inside to a tool like this in order to get the individual tokens/codes: https://github.com/dim13/otpauth

latest google authenticator has an export option. save the url or QR code and you will be able to load it in the next phone (or use a tool such as https://github.com/dim13/otpauth / https://github.com/digitalduke/otpauth-migration-decoder to decode the keys/timers and load in TOTP inside keypassx etc')

The code on this page is a standard otpauth string.

Not tested yet but this tool should allow you to create scanable QR codes for other auth apps as far as I understand. https://github.com/dim13/otpauth

Best KeePass iOS client: KeePassium (by far!)

For the paranoid, there's always KeePass + cloud storage, which is also free. It's what I use. I tend to use KeePassXC, a cross-platform KeePass-compatible application that works on Linux, Mac, and Windows, and I use Dropbox free for my cloud storage, since it actually has a Linux client that works, no hassles, right out of the box. I use KeePassium on my iPhone, and there are plenty of Android KeePass-compatible apps out there, such as KeePassDX, which is open-source and, apparently, very nice. I USED to use KeePass2Android, which the community seems to still like, but I'd probably be using KeePassDX these days since it's fully open-source and available through F-Droid.

I use KeepassXC password manager[1], it keeps my TOTP information and makes it available to use on all my devices. It syncs between my devices using Dropbox. Kepassium[2] makes it available on iOS, and Keepass2Android[3] makes it available on Android. It also manages my SSH keys and adds them to the ssh-agent, even on Windows. and houses a backup of my GPG keys. I even found that it can manage my credentials for use in scripts and git using git-credential-keepassxc[4].

Similar functionality can be had from 1Password[5], of you're into the more fancy experience. As a bonus this approach makes it very easy to store all those backup codes that dotp services often give you. Won't help your current predicament but will prevent it from happening again :)

1: https://keepassxc.org/

2: https://keepassium.com/

3: https://github.com/PhilippC/keepass2android

4: https://github.com/Frederick888/git-credential-keepassxc

5: https://1password.com/

KeePassium - Commercial Open-Source Password Manager for iOS. Free tier available.

For the first question: https://keepassium.com/

I used to use Keepassium last time I had an iPhone, which worked pretty well. You can just copy the database file over, and it never leaves your devices. I agree that you're probably fine with most services, but the extra peace of mind is worth managing a few files manually IMO

Keepassium is great too https://keepassium.com/ if you don't trust Bitwarden. Maybe Bitwarden could get hacked?