Thanks for pointing that out!
You're right — the currently playable modes are BUILD & RACE – STAGE 1-1 and FREE ROAD TRIAL.
The DECK DUEL 1V1 mode is currently unavailable in the public HTML5 build, as it doesn't work correctly in the exported version from Tesana.
I've also updated the game description to make the available modes and the 1V1 limitation clearer. Sorry for the confusion! 🙇♀️