While "LibreOffice 6.3.6" may still be available for download on various third-party mirror sites, it is for general use today:
: Legacy versions do not receive patches for modern security vulnerabilities. LibreOffice-6-3-6-for-Mac-Free-Download--Latest-Version-
: Improved "NotebookBar" (ribbon-style) interface options for users transitioning from Microsoft Office. While "LibreOffice 6
: The current "Fresh" version of LibreOffice (typically 24.x or 7.x) offers significantly better performance, native Apple Silicon support, and modern file compatibility. native Apple Silicon support
: It was designed to run on Intel-based Macs (x86_64). Note that native support for Apple Silicon (M1/M2/M3 chips) only became standard in later major versions (7.x series).