Does auto.arima of the forecast package deal with seasonality and trend automatically
Yes, the aim of auto.arima is for fitting ARIMA models automatically. You do not need to decompose your time series before hand. See how the algorithm works here https://otexts.com/fpp3/arima-r.html.
You may still want to look at arguments available in the auto.arima function, and you may want to change default maximum values for p, q, and d, etc.