Some users reported that Patch 1.02 (not 108 specifically, but close!) or later versions unlock all characters. You can try updating your game to the latest version.
** 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/ street fighter x tekken pc patch 108 character unlock link
** 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). Some users reported that Patch 1
Here are some useful posts and links that might help: street fighter x tekken pc patch 108 character unlock link
Or, visit the Steam Community page for SFxT: https://steamcommunity.com/app/1210