ZTF J210411.01-010202.3 = Gaia21fhx: superoutburst of AM CVn star? Josch Hambsch have reported observations. The object gradually faded from Nov. 28 to Dec. 4, then followed by sudden fading by 1.8 mag on the next night. This fading rate is too large for a hydrogen-rich dwarf nova. This object may be an AM CVn star (or EI Psc star) and further observations are encouraged.