In French noun have a gender and Zwift sounds masculine, and according to Alpe du Zwift, it is. But : “Tour de Zwift” is suggest it is feminine. I know you named it after : “Tour de France”, but France is feminine while Zwift is not. So please name your future events :“Tour du Zwift”. See this answer
https://french.stackexchange.com/a/14356 on Stackexchange, where Zwift as masculine consonant initial (like Danemark in the discussion on stackexchange).
Zwift is actually transgender, depending on the situation.
Trans gender names (épicène) are almost inexistant in French:
" Le Français compte deux genres grammaticaux : le masculin et le féminin. Les mots épicènes y sont minoritaires."
Ask about any French speaking person and they’ll tell you Zwift is masculine, Zwifte would be the feminine version. So it should be either “Tour de Zwifte” or “Tour du Zwift”.
Zwift is not a French word, so you should not use French grammar IMO (your example with Zwift / Zwifte).
@Milan_Rost, Zwift is a proper noun and you are right it is not possible to change the gender of a proper noun.
My point is exactly what you are saying, the name Zwift cannot change gender. Tour de Zwift make the gender of Zwift feminine. So it must be “Tour du Zwift”. If you want to keep Tour de Zwift, Zwift would be feminine thus it should be Zwifte, but nobody want that.
UK is masculine like Zwift and would be Tour du UK so it must be Tour du Zwift.
“Tour of Zwift” also solves the problem.