This is by design that file would be in checked out state when uploading the file if you set Require documents to be checked out to Yes. There is no way to change it. You have to check in the file manually after uploading.
For disabling Name -mandatory column, this only works when Require documents to be checked out is set to No.
Since you have checked the "Require documents to be checked out "option, even if the Document Library does not set the mandatory fields, the file remains checked-out when drag and dropped it.