Aegis covers this use case if you sync the local export via proton drive or other could sync you trust e.g. a self-hosted nextcloud server. Proton should not spend their limited dev time on a problem that already has a good libre/open source solution.

Doing this is a bit of a security improvement over having your TOTP codes in proton pass as they have a separate encryption key from aegis so someone with access to your proton account would still need to ***** the encryption on your aegis vault backup separately. This is less secure than Yubikeys as has been pointed out but of course less vulnerable to locking you out of your stuff if your only copies are lost/destroyed - as usual there's a trade-off.

I would like a standalone authenticator that syncs with ProtonPass for the 2FA keys, possibly secured with a hardware key or maybe a different password or something only for the authenticator to open

Integrating TOTP with Proton Pass is highly beneficial because it automatically copies the TOTP code, making it very convenient to access. Alternatively, Aegis is an open-source option.

This would be a huge thing. The danger with Offline TOTP Apps like Aegis and other are that if you forget to manually back it up, you loose everything if you loose your phone.
I know cases where exactly this happened.
Passwort reset won't help then.
But it needs to be also on Linux (Fedora).

Yes, BUT please add support for the only thing no one else is able to do: “sync” the added codes with Proton Pass so it knows there's a 2FA Code for it (without actually adding the secrets to Pass)

Why not use an open source app like Aegis which supports "indirect" cloud backup ?
No need for Proton to waste resources on such an app...

This would be great, as currently I need to use a third party to sign into my proton account using 2FA.

A dedicated synced 2FA app only to sign into proton would be sufficient, as all other 2FAs could be stored in Proton Pass.

There are already FOSS alternatives to Google/Microsoft Authenticator. There is no reason for Proton to make one.

TOTP is not the best MFA and idealy you would not store the keys for it on any device you will authenticate to
I would simplay recommend using a Yubikyey (maybe two so you have a backup) and keeping the TOTP secret on the yubikey(s) with the Yubico authenricator app
this restores TOTP back to being on a keyfob wich there is a reason it started out on keyfobs is it creates an air-gap where the seed/key/secret can’t be leaked

Just use Aegis. FOSS (as far as I know) and allows backups. Only locally unfortunately, but you can then sync that to your Proton Drive anyway now.

For me, a nicer option would be to allow automatic backups of my Aegis codes to Proton Drive.

It is already available in Proton Pass!

Create an alternative to google authentificator via a mobile application.

Now that I have proton pass I prefer it for 2FA over old-style apps like microsoft authenticator.

The only thing I am concerned about -- the 2FA token is no longer tied to control of a physical object. It is now tied to control of a proton account. Not sure if this is a smart tradeoff for convenience.

2FA is available on Proton Pass, isn’t it?

Would love to stop using Authy in favor of an equivalent Proton product for 2FA. Must run on Desktop, not only mobile!

You might be better off using a hardware based TOTP generator separate from your password manager (and not a cloud based one) like a Yubi 5C with the YubiAuthenticator app.

Proton Pass achieves this as far as I’m aware?

If they made it work just like Google Authenticator with the cloud saving and everything it would be one of the best features of Proton.

Truly, I want my authenticator app to be separate from my password vault app. Until now, I've been using Authy for the longest time but just found out that they are abandoning their desktop app. Proton Plus may have built-in 2FA, but I'm not interested in switching password vaults.