Okay, so do I did some digging and there is a good news for you. Though it is incremental after 1st go, and there is no way to change it, I checked. Here, these incremental backups are not the traditional incremental backups we know of. They work a little different and no backups are dependent on each here.

For more details checked the answer in forums by lead Dev : https://forum.duplicati.com/t/backup-type-is-incremental/8786/3?u=fedonr

And also here it is by a Contributor who manages their documentation: https://github.com/duplicati/duplicati/issues/3182#issuecomment-382128082