Try booting into Safe Mode to see if that helps. If not, then while booted into Safe Mode disconnect the laptop from the network in case the issue is due to some cloud service. You do not want to run out of space on an APFS volume or you will have problems. If an APFS volume runs out of free space, then you will not be able to delete anything in order to free up space due to how the APFS file system works and Apple's poor implementation by overlooking the need to permanently reserve a small amount of space for system use so files can be deleted.
If this is able to stop the free space from being consumed, then make sure you have a good backup before doing anything else since that should be the first priority if you don't have backups.
You will want to check Activity Monitor on the "Disk" tab to see which app/process is writing the most data. Within Activity Monitor click the "View" menu and select "All Processes" since it may be a system level process which is normally hidden from view.
FYI, you need to keep at least 20GB+ of free storage space available at all times for the normal operation of macOS. Some workloads may require even more free space. As you have discovered, sometimes that free space can be consumed quickly.
