# tmutil listlocalsnapshots /
Snapshots for volume group containing disk /:
com.apple.TimeMachine.2022-04-15-221945.local
com.apple.TimeMachine.2022-04-15-232409.local
com.apple.TimeMachine.2022-04-16-002311.local
com.apple.TimeMachine.2022-04-16-012006.local

# tmutil deletelocalsnapshots 2022-04-15-221945
Deleted local snapshot '2022-04-15-221945'

or delete all backups as oneliner:

# echo "local backups:";tmutil listlocalsnapshots / ; echo "delete: " ; tmutil listlocalsnapshots / | tail -n +2 | sed -e 's/com\.apple\.TimeMachine\.\(.*\)\.local/\1/' | while read line ; do tmutil deletelocalsnapshots $line ; done