Here are some useful posts and links that might help:
You can download the patch from the official Capcom website: http://www.capcom.com/support/sfxtpc_patch.html
Capcom released an official patch for Street Fighter X Tekken on PC, which includes various bug fixes, balance changes, and... character unlocks ! street fighter x tekken pc patch 108 character unlock link
** GameFAQs and Steam Community:** You can also check the GameFAQs page for Street Fighter X Tekken on PC: https://gamefaqs.gamespot.com/pc/2420-street-fighter-x-tekken/
Keep in mind that some of these links or tools might not be up-to-date or supported by Capcom. Be cautious when downloading or using third-party patches. Here are some useful posts and links that
** Unofficial Patch and Tools:** Alternatively, you can try using third-party tools or patches, like the " Character Unlocker" or "SFxT Character Unlock Tool" (be cautious when using these, as they might not be officially supported).
Or, visit the Steam Community page for SFxT: https://steamcommunity.com/app/1210 Be cautious when downloading or using third-party patches
Some Reddit users shared a link to a thread with a : https://www.reddit.com/r/StreetFighterXTekken/comments/1jyy13/character_unlock_tool/