How do I clear disk space on Mac OS Catalina? diskutil shows

Container Total Space:     250.1 GB (250135076864 Bytes) (exactly 488545072 512-Byte-Units)
Container Free Space:      10.1 GB (10112528384 Bytes) (exactly 19751032 512-Byte-Units)


Finder says I have 48.56 GB available. Any suggestions for the 38 GB difference?

Catalina beta 4 won't download until I clear more space.
The difference is almost always TimeMachine snap shots.

For more info see https://support.apple.com/en-us/HT204015