I looked a bit further, after being stumped. It looks like this is available in the alpha release of Tor, not the stable release. Looks like Tor has been working to move this into stable relatively recently:
I found more details from the link to the documentation wiki, where it informs that
Snowflake is included in alpha releases of Tor Browser.
Sorry for the bother, hope someone else here finds this interesting
Edit: Here are some screenshots for using the Snowflake proxy feature in Tor. I am actually using it to submit this edit!
First, select “configure” when starting Tor for the first time:
Then, select “snowflake” from the dropdown menu: