There is no Apple-defined amount of storage that /System/Volume/ Data should always occupy, so 30 GB should not be considered a required or universally “healthy” amount.
/System/Volume/ Data is a broad storage category used for files that do not fit into the other categories shown in macOS Storage settings.
According to Apple, it can include caches, log files, virtual-memory files, temporary files, application support files, plug-ins, and other system resources. Its size can therefore change over time.
You can review your storage in Apple menu >> System Settings >> General >> Storage.
You also us Finder >> Go >> Utilities >> Disk Utilities to see Free Space versus Used Space
Manage storage space on your Mac
Cloud storage can also be relevant when reviewing available space.
A file stored in iCloud or another cloud service may also have data stored locally on the Mac.
With iCloud, macOS can use storage optimization to store some content in iCloud and make it available when needed.
As a result, the amount of data in your cloud account may differ from the amount of storage currently used on the Mac.
Free up storage space on your Mac
It is also important to distinguish between the System Data category and the underlying APFS volumes.
They are not the same thing.
On current versions of macOS, the startup disk normally includes a system volume and a separate Data volume, commonly named Macintosh HD - Data.
These volumes share available space within the same APFS container. Data shown on the Data volume should therefore not automatically be regarded as System Data.
Learn about APFS volumes in Disk Utility
Because you work with photos and videos, it may be useful to periodically review the storage used by your applications and cloud-storage services.
Where an application provides its own storage-management options, using those options may be preferable to manually deleting files from system locations.
It is generally best not to delete files from the System or Library folders solely to reduce the System Data figure, as these locations can contain files required by macOS or installed applications.
If you use Time Machine, local snapshots may also be relevant when reviewing available storage. Apple explains that macOS manages these snapshots and can remove them when space is needed.
About Time Machine local snapshots on Mac
If System Data becomes unusually large again, consider reviewing the Storage information before making significant changes, such as erasing the Mac. A screenshot of System Settings → General → Storage, and the available volume information, taken before making changes may help distinguish between a large System Data category, ordinary data stored on the Data volume, and files retained locally by a cloud-storage service.
