Fill DS 160 before joining new employer - H1B Transfer

My H1 was activated on October 1,2019. I got an offer and the new employer started a H1 transfer. The transfer is approved and I am joining in November.

I was filling DS160 so that I can book appointment early in India. In the present employer section, if I enter start date as a future date, it does not allow. Should I fill DS 160 only after joining new employer ?

Yes, it is recommended that you fill it out after you join the new employer to avoid issues. You can try to fill it out with current details and then later fill out a new DS-160 as well after November 1st.