How incremental backup and recovery work?

Hi! I tried to backup the cluster to the S3 storage bucket. Firstly, I successfully backed up all the data to the bucket using full backup.

fdbbackup start --cluster-file /etc/foundationdb/fdb.cluster --logdir /fdb-sdbk/log/ --knob_http_request_aws_v4_header=true --knob_http_verbose_level=4 --blob-credentials /credential_files -d "blobstore://minio_access_key@" -w

The backup bucket directory structure is as follows:

├── backups
│   └── all
│   └── xl.meta
└── data
└── all
├── kvranges
│   └── snapshot.000000000765201137
│   └── 0
│   └── range,765245662,1ddebb6945315de5910dcce975a128f9,1048576
│   └── xl.meta
├── logs
│   └── 0000
│   └── 0000
│   └── log,765201137,785201137,44b4ac739f84aa7768e216b4d6a7dca4,1048576
│   └── xl.meta
└── snapshots
└── snapshot,765245662,765245662,2301
└── xl.meta

14 directories, 4 files

Then write new data to the cluster and use parameter --incremental for incremental backup.

fdbbackup start --cluster-file /etc/foundationdb/fdb.cluster --incremental --logdir /fdb-sdbk/log/ --knob_http_request_aws_v4_header=true --knob_http_verbose_level=4 --blob-credentials /credential_files -d "blobstore://minio_access_key@" -w

However, after executing the above command, there were no changes to the backup bucket files and directories.
When I use incremental restore to another cluster, the data also does not exist.

fdbrestore start --dest-cluster-file /etc/foundationdb/fdb.cluster --incremental --logdir /fdb-sdbk/log/ --knob_http_request_aws_v4_header=true --knob_http_verbose_level=4 --blob-credentials /credential_files -r "blobstore://minio_access_key@" -w

When I used full restore, it only restored the data from my first full backup, and the incremental backup data was also lost. It does not appear to have been incrementally backed up?