[kuroguro]

If you root your phone you can get the secret out and use it with regular TOTP software that implements that variant (I forgot the name - I just know Bitwarden supports it).

[pzmarzly]

There are some desktop implementations of Steam TOTP client, so you don't even need a rooted phone, as long as you trust some random open source code. https://github.com/KeeTrayTOTP/KeeTrayTOTP#documentation

[kuroguro]

> In the case of Steam Mobile Authenticator the new output format was reverse engineered by various developers

Oh, so it was a custom one! Was convinced that it was a less used standard algo.