_t omitted variable in XTITSA command

[Dayla Spassio]

I am using XTITSA ( by Ariel Linden - Ariel Linden ) command to study the effect of the Covid-19 pandemic on business profitability

Y= dependent variable (ROI-percentage)
years = time variable (2013 to 2022)
However, I do not understand why the variable _t is omitted

Thanks