I have 117Gb of other files on a disk that is 250Gb, I can not see what it is. How can I get an insight into what it is and remove unwanted content

Try rebuilding Spot light reindexing. https://support.apple.com/en-us/HT201716

A user has no control over “Other” category of storage.

• Other: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.

       https://support.apple.com/guide/system-information/see-available-storage-space-syspf9b375b9/11.0/mac/11

What a user can do?

   1.  Delete files

       https://support.apple.com/guide/system-information/find-and-delete-files-syspf5a64aa6/11.0/mac/11.0

  2.  Optimize storage

       Click the “Manage”button. Wait until Green “Completed” button appears.

       https://support.apple.com/guide/system-information/optimize-storage-space-sysp4ee93ca4/11.0/mac/11.0 

 3.  How to free up storage space on your Mac

      Try all steps posted in this article

      https://support.apple.com/en-us/HT206996

That is probably due to local snapshots. You can’t actually delete files any more. The operating system decides when it will delete files when free disk space gets low.