macOS: Can another user recover files I've deleted?
There are various ways how this can be done:


They may simply have a background job running which regularly copies all your files (whether in Trash or still in Documents etc) into a folder they control
They may use the backups created by Time Machine or any other backup software used
They can use data recovery software to recover deleted files


However, this doesn't necessarily mean that the other person is reading your files.

If you are concerned about the sensitivity of data/files, you are advised to take measures such as using an encrypted volume, not creating files locally, using an external drive to store and view files and additionally, using Private browsing mode in Web browsers etc.