It means LibreOffice changed its versioning scheme last year, so there aren’t 17 releases between 7.4 and 24.8: 7.5, 7.6, 24.2, and 24.8 (25.2 is in preparation). Releases now use a date-based scheme (year using two digits, and month).
A given release of Debian generally includes the version of packages it ships as they were at the time it was frozen; for Debian 12 that was early in 2023.
Newer releases of LibreOffice are made available for Debian 12 in backports. Interestingly in light of your question, LibreOffice themselves recommend that users use the previous release, not the latest one:
The latest release of LibreOffice, recommended for technology enthusiasts, early adopters and power users, which contains new features and program enhancements.
The more mature previous release of LibreOffice, recommended for corporate implementations and more cautious users. As such, the version is stable and is suitable for all users.