MacBook Pro: Settings crashes, low disk space

Fix in order:

1. Delete local snapshots
2. Clear caches
3. Remove local iCloud Drive downloads
4. Boot Safe Mode
5. Reset System Preference plist files
6. Turn off “Optimize Mac Storage” once Settings works again

Your Mac will stop crashing and you’ll recover tens of GB of actual usable space.

Do the calculations (11gb of a 250gb drive)

11 GB divided by 256 GB =238.419 GB , about 4 % of the Total Drive Capacity is Free Space

The general run is to keep about 15 -20 Percent of the Total Drive Capacity as Free Space

There are some who suggest a minimum of 100 GB as Free Space

Reducing System/Volume/Data is a common question. 

1 -  System data taking too much in MacOS Sono… - Apple Community

2 - Time Machine Local Snapshot won't delete - Apple Community

3 - Over 60% storage blocked by System Data - Apple Community

How to free up ‘System Data’ and other storage on your Mac from a fellow colleague  @ neuroanatomist

Use another application to see where space is being used  Storeograph  on the Apple Apps Store 

Suggest getting an External SSD Drive and start moving your Pictures, Videos, Music and any other large files you have control over, OFF the Internal drive and Onto the External

There are  two effective ways to remedy this issue:

1. Quick Fix Actions:

For Apple Intel computers, use Disk Utility to erase an Intel-based Mac, then reinstall macOS.

Always make a Time Machine backup before proceeding.

Migrate only the user account, not the entire system.

Reinstall only the necessary applications from the Apple App Store or directly from the developers.

2 - Generally

When the user discovers this issue, it’s likely because the computer’s internal drive capacity is small, such as 256 GB

Unfortunately, the user’s storage needs may have increased since the computer was purchased.

To future-proof the computer, consider spending extra money upfront on a larger drive capacity and adding more unified RAM.

Follow on

OP wrote " On rebooting again 'About this Mac' suggests I have 42.6gb free??? Hope someone can help."

Possible as the Operating System may have >>

From another contributor @etresoft regarding Free Space and Available Space 

Free vs available disk space huge differe… - Apple Community

Quote >>  “ The "available" storage is the amount of used storage that the operating system could automatically delete if it felt that it was really necessary.

The "free" storage is the amount that you can actually use for something.

There are system processes that run in the background and automatically delete some of the "available" storage and convert it to "free". If you completely run out of storage, then those system processes will try a little harder. When you "delete" files you are just hinting to the operating system that you don't need those files anymore. The operating system will eventually remove them, but on its own schedule.

Certain tools will allow you to force the issue and manually clean up some of this storage and manually delete local snapshots. But that is only temporary. "  << End Quote 

Purgeable Space is controlled by the Operating System and not the user 

Get detailed information about a disk in Disk Utility on Mac