Refer to LibreOffice lock files and Dropbox
The referenced question/answers did not have complete information. I talked to Dropbox and they very satisfactorily explained that they do not synchronize hidden/system files because those files are used/named differently on different operating systems.
AutoCAD’s file locking system, for comparison, uses *.dwl and *.dw2 files (in the past ten years, AutoCAD added a second redundant lock file because they wanted one in XML format and they preserved also the legacy lock file) that are plain text and visible. This locking system syncs find with Dropbox.
Would it be possible for LibreOffice to add a lock file system that has plain (synchronhizable) names and plain-text contents?