Does it support Steam style tokens?

YES!

TL;DR

Use this guide to get your Steam token secret, then use one of the following CLI commands to add Steam token:

• totp add token_name -a steam -d 5 -e base64 - if your Steam secret token looks Base64-encoded (has alpha-numeric characters in different case lower and upper)
• totp add token_name -a steam -d 5 -e base32 - if your Steam secret token looks Base32-encoded (has alpha-numeric characters all in the same case, either all lower or all upper)

Details

Steam has special token format which contains 5 alpha-numeric characters.

Flipper Authenticator support this type of tokens. To add such a token it is necessary to pick Steam algorithm and 5-character length whenever you are adding new token.

It is a bit trick to get token secret, so you'd better use this guide to do that.

Keep in mind that by default Flipper Authenticator expects you to provide any secret as Base32-encoded string, while Steam token typically (but not all the time) Base64-encoded. Just in case if your Steam token secret is Base64-encoded and you are using CLI to add new token, there is no need to manually convert it to Base32, instead just add -e base64 option to your CLI command, it will force Authenticator app to read your token as Base64-encoded string.