tmclone.sh

#!/bin/bash
# The script can copy part of TimeMachine folders from one to another place.
# In the way like TM does. Next folder contains just difference.
# Unfortunatry the target folder will take more space. Becase of rsync doesn't support hard links for folders.

BYPASS=/System/Library/Extensions/TMSafetyNet.kext/Contents/Helpers/bypass
RSYNC=/usr/local/bin/rsync  # Path to rsync. By default in MacOS it's version 2.
RSYNC2_ARGS="--extended-attributes"
RSYNC3_ARGS="--xattrs --acls --crtimes --one-file-system --numeric-ids"
RSYNC_ARGS="--archive --progress -P --human-readable --update --stats --verbose --inplace"

SRC="/Volumes/SrouceTimeMachine"  # Source TimeMachine disk
DST="/Volumes/TargetTimeMachine"  # Target TimeMachine disk
BDIR="Backups.backupdb"

DATES_MASKS="2021-*"  # Folder mask on to copy

MACHINE_NAME=$(ls -d $SRC/$BDIR/*)
MACHINE_NAME=$(basename "$MACHINE_NAME")

# The script works only with one device time machine archive
SRC_DATES=""
for mask in $DATES_MASKS; do
    for folder in $SRC/$BDIR/"$MACHINE_NAME"/$mask; do
        echo "Add folder $folder to queue"
        SRC_DATES="$SRC_DATES $(basename "$folder")"
    done
done

if $RSYNC --version | grep -q 'rsync  version 3'; then
    echo "You have rsync 3"
    RUN_RSYNC="$RSYNC $RSYNC3_ARGS $RSYNC_ARGS"
else
    echo "You have rsync 2"
    RUN_RSYNC="$RSYNC $RSYNC2_ARGS $RSYNC_ARGS"
fi

echo "Add bypass"
RUN_RSYNC="$BYPASS $RUN_RSYNC"

echo "Sync $BDIR"
echo "You can find progess in log file sync_log_$BDIR"

echo $RUN_RSYNC --exclude \""$BDIR/"$MACHINE_NAME"/*"\" "$SRC/$BDIR" "$DST" 2\>\&1 \> sync_log_$BDIR
$RUN_RSYNC --exclude "$BDIR/$MACHINE_NAME/*" "$SRC/$BDIR" "$DST" 2>&1 > sync_log_$BDIR

first=true
for curr in $SRC_DATES; do
    if [ "$first" = true ]; then
        echo "Sync $curr folder"
        echo "You can find progess in log file sync_log_$curr"
        echo $RUN_RSYNC "$SRC/$BDIR/$MACHINE_NAME/$curr" "$DST/$BDIR/$MACHINE_NAME/" 2\>\&1 \> sync_log_$curr
        $RUN_RSYNC "$SRC/$BDIR/$MACHINE_NAME/$curr" "$DST/$BDIR/$MACHINE_NAME/" 2>&1 > sync_log_$curr
        prev=$curr
        first=false
        continue
    fi
    echo "Sync $curr folder"
    echo "You can find progess in log file sync_log_$curr"
    echo $RUN_RSYNC --link-dest=../$prev/ "$SRC/$BDIR/$MACHINE_NAME/$curr/" "$DST/$BDIR/$MACHINE_NAME/$curr/" 2\>\&1 \> sync_log_$curr
    $RUN_RSYNC --link-dest=../$prev/ "$SRC/$BDIR/$MACHINE_NAME/$curr/" "$DST/$BDIR/$MACHINE_NAME/$curr/" 2>&1 > sync_log_$curr
    prev=$curr
done

Context: https://apple.stackexchange.com/a/422061
#thx