I’m new to Hestia and I ran into the same issue… I found I had to enable incremental backups in the package settings assigned to my user (and admin) accounts:
Once I did that, I was able to see the Incremental Backup button in the backup section. I also added this to my panel cron jobs to run incremental backups once a day:
10 05 * * * sudo /usr/local/hestia/bin/v-backup-users-restic
I set the regular “v-backup-users” to run once a week, and the incremental backups to run daily. I sync everything to a Backblaze S3 bucket via rclone. Hope that helps!