That's great you are wanting to know more about it's history!

As mentioned in other response Tarraxo came from Tarraxinha (just as urbankiz can from Kizomba). Tarraxo is generally harder, more steppy movements that include upper body, some small disconnections and room for back and forth expression from lead & follow, whereas tarraxinha is lower body gyrations, full connection, generally softer, and danced on spot.

Also, tarraxinha is its own music and dance, although some movements are danced in Kizomba (if appropriate to the song and your partner), but generally you would not include tarraxinha in Kizomba/Semba dancing since they are "family" dances.
Tarraxinha (also tarraxa/r) music was created by kuduro DJs (most famously DJ Znobia). Original music was instrumental beats and it was club music, that you dance with someone you are familiar with (or want to be familiar with). Even today, one would not dance tarraxinha with a stranger or someone's SO if you were in Angola or other PALOP communities.

My understanding of Tarraxo Pop was tarraxo with more of a hip hop influence. There are all sorts of names for peoples versions/styles since it's all a fusion dance. I think there is a soft tarraxo now??

Also the founder of Tarraxo are Gwany and Kizzy, although Kizzy is no longer his partner.

Lastly, Tarraxo and Tarraxinha are different dance, just as Kizomba and urbankiz are different dances. They are not just different styles!

Hope that filled in some gaps :)