Does new H4 visa need to be applied through in person or can he be eligible for dropbox also

I am in USA and have my H1B transfer was done also I’m working with new employer from 2 months. My spouse had H4visa of previous employer with stamping validility until 2023 october. Now he was in INDIA and willing to travel in June.

  1. When I asked my current employer for H4 transfer, they replied to apply for new H4 visa at US Embassy located at INDIA. So does he not required to apply for H4 transfer like H1B transfer process happens. Also will he be eligible for dropbox as he had his recent H4 visa stamping done in December 2021 with my previous employer
  2. If not required will he be able to fill DS160 form and directly choose for Dropbox (or) he need to go for in person interview.
    3)As slots are not available in INDIA nearby can he travel with previous H4 stamped visa and carry documents of my new employer I 797 approval copy , pay stubs copy etc
    Please help to clear on these things.
    Thank You

First of all, H4 is independent of employer, rather it is a derivative of primary H1B.
When you apply for H1B change of employer petition aka transfer, you have to do extension of status for H4 however it applies only if H4 is present in the US.

In your case as the H4 already have a valid visa till 2023, H4 can travel to the US as far as the visa is valid.
Have the H4 carry below documents that can be presented to the CBP/immigration officer at port of entry while entering the US.
Copy of primary H1B I-797
Copy of primary H1B employment verification letter.
Last three pay stubs for primary H1B.
Marriage certificate
Marriage photo album
H4 current passport with valid H4 visa.

No need of H4 visa is still valid at the time of travel to the US.

Correct, refer above.